EF Core 2.0中开启Transaction事务会对DbContext创建和关闭数据库连接的行为有所影响

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数据库


 

我们先在SQL Server数据库中建立一个Book表:

CREATE TABLE [dbo].[Book](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [BookName] [nvarchar](50) NULL,
    [BookDescription] [nvarchar](50) NULL,
    [ISBN] [nvarchar](20) NULL,
    [CreateTime] [datetime] NULL,
 CONSTRAINT [PK_Book] PRIMARY KEY CLUSTERED 
(
    [ID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO

ALTER TABLE [dbo].[Book] ADD  CONSTRAINT [DF_Book_CreateTime]  DEFAULT (getdate()) FOR [CreateTime]
GO

然后插入如下数据:

INSERT [dbo].[Book] ([BookName], [BookDescription], [ISBN]) VALUES (N\'Chinese\', N\'Chinese\', N\'0001\')
GO
INSERT [dbo].[Book] ([BookName], [BookDescription], [ISBN]) VALUES (N\'English\', N\'English\', N\'0002\')
GO
INSERT [dbo].[Book] ([BookName], [BookDescription], [ISBN]) VALUES (N\'Japanese\', N\'Japanese\', N\'0003\')
GO
INSERT [dbo].[Book] ([BookName], [BookDescription], [ISBN]) VALUES (N\'Russian\', N\'Russian\', N\'0004\')
GO
INSERT [dbo].[Book] ([BookName], [BookDescription], [ISBN]) VALUES (N\'Italian\', N\'Italian\', N\'0005\')
GO

查询Book表的数据,如下图所示:

 

现在我们使用EF Core将Book表映射到.NET Core控制台项目中的Book实体上,Book实体如下所示:

using System;
using System.Collections.Generic;

namespace EFCoreDB.Entities
{
    public partial class Book
    {
        public int Id { get; set; }
        public string BookName { get; set; }
        public string BookDescription { get; set; }
        public string Isbn { get; set; }
        public DateTime? CreateTime { get; set; }
    }
}

 

不使用事务


 

然后我们在.NET Core控制台项目Program类的Main方法中,使用DbContext(也就是FinanceDigitalToolContext)读取BookName为"Chinese"的Book实体,然后使用DbContext.SaveChanges方法两次更改其BookDescription属性的值,再从数据库中将其查询出来显示,代码如下:

using EFCoreDB.Entities;
using System;
using System.Linq;
using System.Linq.Expressions;

namespace EFCoreDB
{
    class Program
    {
        static void Main(string[] args)
        {
            using (FinanceDigitalToolContext dbContext = new FinanceDigitalToolContext())
            {
                Expression<Func<Book, bool>> bookExpression = b => b.BookName == "Chinese";//构造查询条件,来查询BookName为Chinese的Book

                var chineseBook = dbContext.Book.First(bookExpression);//获取BookName为Chinese的Book实体chineseBook

                chineseBook.BookDescription = "This is a Chinese book";//更改chineseBook的BookDescription属性
                dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库

                chineseBook.BookDescription = "This is a very good Chinese book";//再次更改chineseBook的BookDescription属性
                dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库

                chineseBook = dbContext.Book.First(bookExpression);//重新获取BookName为Chinese的Book实体chineseBook

                //显示当前chineseBook的当前BookDescription属性值
                Console.WriteLine(chineseBook.BookName + " book has description: \\"" + chineseBook.BookDescription + "\\"");
            }

            Console.WriteLine("Press key to quit....");

            Console.ReadLine();
        }
    }
}

执行上面的代码,我们使用EF Core的日志功能,输出每次DbContext访问数据库时的后台日志信息:

 

首先在执行

var chineseBook = dbContext.Book.First(bookExpression);//获取BookName为Chinese的Book实体chineseBook

时,EF Core的日志如下所示:

=============================== EF Core log started ===============================
Opening connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Opened connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executing DbCommand [Parameters=[], CommandType=\'Text\', CommandTimeout=\'30\']
SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]
FROM [Book] AS [b]
WHERE [b].[BookName] = N\'Chinese\'
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executed DbCommand (129ms) [Parameters=[], CommandType=\'Text\', CommandTimeout=\'30\']
SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]
FROM [Book] AS [b]
WHERE [b].[BookName] = N\'Chinese\'
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
A data reader was disposed.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Closing connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Closed connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Context \'Book\' started tracking \'FinanceDigitalToolContext\' entity. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see key values.
=============================== EF Core log finished ===============================

从日志中我们可以看出来,dbContext.Book.First(bookExpression)在数据库中开启了一个数据库连接,并使用SQL语句做了查询,然后关闭了数据库连接。

 

然后在执行下面的代码

chineseBook.BookDescription = "This is a Chinese book";//更改chineseBook的BookDescription属性
dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库

时,EF Core的日志如下所示:

=============================== EF Core log started ===============================
SaveChanges starting for \'FinanceDigitalToolContext\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
DetectChanges starting for \'FinanceDigitalToolContext\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Unchanged \'Book.BookDescription\' detected as changed and will be marked as modified. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see property values.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
An \'Book\' entity tracked by \'FinanceDigitalToolContext\' changed from \'Unchanged\' to \'Modified\'. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see key values.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
DetectChanges completed for \'FinanceDigitalToolContext\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Opening connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Opened connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Beginning transaction with isolation level \'ReadCommitted\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executing DbCommand [Parameters=[@p1=\'?\' (DbType = Int32), @p0=\'?\' (Size = 50)], CommandType=\'Text\', CommandTimeout=\'30\']
SET NOCOUNT ON;
UPDATE [Book] SET [BookDescription] = @p0
WHERE [ID] = @p1;
SELECT @@ROWCOUNT;
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executed DbCommand (86ms) [Parameters=[@p1=\'?\' (DbType = Int32), @p0=\'?\' (Size = 50)], CommandType=\'Text\', CommandTimeout=\'30\']
SET NOCOUNT ON;
UPDATE [Book] SET [BookDescription] = @p0
WHERE [ID] = @p1;
SELECT @@ROWCOUNT;
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
A data reader was disposed.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Committing transaction.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Closing connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Closed connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Disposing transaction.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
An \'Book\' entity tracked by \'FinanceDigitalToolContext\' changed from \'Modified\' to \'Unchanged\'. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see key values.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
SaveChanges completed for \'FinanceDigitalToolContext\' with 1 entities written to the database.
=============================== EF Core log finished ===============================

从日志中我们可以看出来在执行dbContext.SaveChanges方法时,EF Core在数据库中开启了一个数据库连接,并使用SQL语句做了数据库更改,然后关闭了数据库连接。然后chineseBook这个Book实体的EntityState从Modified变为了Unchanged。

 

然后执行代码

chineseBook.BookDescription = "This is a very good Chinese book";//再次更改chineseBook的BookDescription属性
dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库

时,EF Core的日志如下所示:

=============================== EF Core log started ===============================
SaveChanges starting for \'FinanceDigitalToolContext\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
DetectChanges starting for \'FinanceDigitalToolContext\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Unchanged \'Book.BookDescription\' detected as changed and will be marked as modified. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see property values.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
An \'Book\' entity tracked by \'FinanceDigitalToolContext\' changed from \'Unchanged\' to \'Modified\'. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see key values.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
DetectChanges completed for \'FinanceDigitalToolContext\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Opening connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Opened connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Beginning transaction with isolation level \'ReadCommitted\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executing DbCommand [Parameters=[@p1=\'?\' (DbType = Int32), @p0=\'?\' (Size = 50)], CommandType=\'Text\', CommandTimeout=\'30\']
SET NOCOUNT ON;
UPDATE [Book] SET [BookDescription] = @p0
WHERE [ID] = @p1;
SELECT @@ROWCOUNT;
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executed DbCommand (19ms) [Parameters=[@p1=\'?\' (DbType = Int32), @p0=\'?\' (Size = 50)], CommandType=\'Text\', CommandTimeout=\'30\']
SET NOCOUNT ON;
UPDATE [Book] SET [BookDescription] = @p0
WHERE [ID] = @p1;
SELECT @@ROWCOUNT;
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
A data reader was disposed.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Committing transaction.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Closing connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Closed connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Disposing transaction.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
An \'Book\' entity tracked by \'FinanceDigitalToolContext\' changed from \'Modified\' to \'Unchanged\'. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see key values.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
SaveChanges completed for \'FinanceDigitalToolContext\' with 1 entities written to the database.
=============================== EF Core log finished ===============================

同样从日志中我们可以看出来在执行dbContext.SaveChanges方法时,EF Core在数据库中开启了一个数据库连接,并使用SQL语句做了数据库更改,然后关闭了数据库连接。然后chineseBook这个Book实体的EntityState从Modified变为了Unchanged。

 

然后执行代码

chineseBook = dbContext.Book.First(bookExpression);//重新获取BookName为Chinese的Book实体chineseBook

时,EF Core的日志如下所示:

=============================== EF Core log started ===============================
Opening connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Opened connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executing DbCommand [Parameters=[], CommandType=\'Text\', CommandTimeout=\'30\']
SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]
FROM [Book] AS [b]
WHERE [b].[BookName] = N\'Chinese\'
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executed DbCommand (21ms) [Parameters=[], CommandType=\'Text\', CommandTimeout=\'30\']
SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]
FROM [Book] AS [b]
WHERE [b].[BookName] = N\'Chinese\'
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
A data reader was disposed.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Closing connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Closed connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================

从日志中我们可以看出来,dbContext.Book.First(bookExpression)在数据库中还是开启了一个数据库连接,并使用SQL语句做了查询,然后关闭了数据库连接。

 

总结下来,上面的代码和日志发生的事情如下:

  • dbContext.Book.First(bookExpression)开启和关闭了一个数据库连接,查询BookName为Chinese的Book实体chineseBook
  • 第一个dbContext.SaveChanges()开启和关闭了一个数据库连接,更改chineseBook的BookDescription属性值"This is a Chinese book"到数据库
  • 第二个dbContext.SaveChanges()开启和关闭了一个数据库连接,更改chineseBook的BookDescription属性值"This is a very good Chinese book"到数据库
  • dbContext.Book.First(bookExpression)开启和关闭了一个数据库连接,重新查询BookName为Chinese的Book实体chineseBook

所以综上所述DbContext一共开启了和关闭了四个数据库连接。

 

 

使用事务


 

现在我们更改Program类Main方法中的代码,将两次DbContext.SaveChanges方法的调用都放在一个TransactionScope事务范围中,所以现在两次DbContext.SaveChanges方法提交的SQL都会在同一个数据库事务中,代码如下所示:

using EFCoreDB.Entities;
using System;
using System.Linq;
using System.Linq.Expressions;
using System.Transactions;

namespace EFCoreDB
{
    class Program
    {
        static void Main(string[] args)
        {
            using (FinanceDigitalToolContext dbContext = new FinanceDigitalToolContext())
            {
                Expression<Func<Book, bool>> bookExpression = b => b.BookName == "Chinese";//构造查询条件,来查询BookName为Chinese的Book

                var chineseBook = dbContext.Book.First(bookExpression);//获取BookName为Chinese的Book实体chineseBook

                //使用TransactionScope事务范围来开启一个数据库事务
                using (TransactionScope transactionScope = new TransactionScope(TransactionScopeOption.RequiresNew))
                {
                    chineseBook.BookDescription = "This is a Chinese book";//更改chineseBook的BookDescription属性
                    dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库,由于TransactionScope事务范围的存在,所以DbContext.SaveChanges方法提交的SQL语句都存在于TransactionScope的事务当中

                    chineseBook.BookDescription = "This is a very good Chinese book";//再次更改chineseBook的BookDescription属性
                    dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库,由于TransactionScope事务范围的存在,所以DbContext.SaveChanges方法提交的SQL语句都存在于TransactionScope的事务当中

                    transactionScope.Complete();//提交TransactionScope事务范围中的SQL语句到数据库,数据库事务结束
                }

                chineseBook = dbContext.Book.First(bookExpression);//重新获取BookName为Chinese的Book实体chineseBook

                //显示当前chineseBook的当前BookDescription属性值
                Console.WriteLine(chineseBook.BookName + " book has description: \\"" + chineseBook.BookDescription + "\\"");
            }

            Console.WriteLine("Press key to quit....");

            Console.ReadLine();
        }
    }
}

执行上面的代码,我们还是使用EF Core的日志功能,输出每次DbContext访问数据库时的后台日志信息:

 

首先执行

var chineseBook = dbContext.Book.First(bookExpression);//获取BookName为Chinese的Book实体chineseBook

时,EF Core的日志如下所示:

=============================== EF Core log started ===============================
Opening connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Opened connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executing DbCommand [Parameters=[], CommandType=\'Text\', CommandTimeout=\'30\']
SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]
FROM [Book] AS [b]
WHERE [b].[BookName] = N\'Chinese\'
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executed DbCommand (139ms) [Parameters=[], CommandType=\'Text\', CommandTimeout=\'30\']
SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]
FROM [Book] AS [b]
WHERE [b].[BookName] = N\'Chinese\'
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
A data reader was disposed.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Closing connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Closed connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Context \'Book\' started tracking \'FinanceDigitalToolContext\' entity. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see key values.
=============================== EF Core log finished ===============================

从日志中我们可以看出来,dbContext.Book.First(bookExpression)在数据库中开启了一个数据库连接,并使用SQL语句做了查询,然后关闭了数据库连接。

 

然后执行

using (TransactionScope transactionScope = new TransactionScope(TransactionScopeOption.RequiresNew))
{

TransactionScope的事务范围开始,此时数据库事务已经开始,EF Core没有输出日志

 

然后执行

chineseBook.BookDescription = "This is a Chinese book";//更改chineseBook的BookDescription属性
dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库,由于TransactionScope事务范围的存在,所以DbContext.SaveChanges方法提交的SQL语句都存在于TransactionScope的事务当中

时,EF Core的日志如下所示:

=============================== EF Core log started ===============================
SaveChanges starting for \'FinanceDigitalToolContext\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
DetectChanges starting for \'FinanceDigitalToolContext\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Unchanged \'Book.BookDescription\' detected as changed and will be marked as modified. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see property values.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
An \'Book\' entity tracked by \'FinanceDigitalToolContext\' changed from \'Unchanged\' to \'Modified\'. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see key values.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
DetectChanges completed for \'FinanceDigitalToolContext\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Opening connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Opened connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Enlisted in an ambient transaction with isolation level \'Serializable\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executing DbCommand [Parameters=[@p1=\'?\' (DbType = Int32), @p0=\'?\' (Size = 50)], CommandType=\'Text\', CommandTimeout=\'30\']
SET NOCOUNT ON;
UPDATE [Book] SET [BookDescription] = @p0
WHERE [ID] = @p1;
SELECT @@ROWCOUNT;
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executed DbCommand (79ms) [Parameters=[@p1=\'?\' (DbType = Int32), @p0=\'?\' (Size = 50)], CommandType=\'Text\', CommandTimeout=\'30\']
SET NOCOUNT ON;
UPDATE [Book] SET [BookDescription] = @p0
WHERE [ID] = @p1;
SELECT @@ROWCOUNT;
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
A data reader was disposed.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
An \'Book\' entity tracked by \'FinanceDigitalToolContext\' changed from \'Modified\' to \'Unchanged\'. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see key values.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
SaveChanges completed for \'FinanceDigitalToolContext\' with 1 entities written to the database.
=============================== EF Core log finished ===============================

从日志中我们可以看出来在执行dbContext.SaveChanges方法时,EF Core在数据库中开启了一个数据库连接,并使用SQL语句做了数据库更改,但是没有关闭数据库连接。然后chineseBook这个Book实体的EntityState从Modified变为了Unchanged。

 

然后执行

chineseBook.BookDescription = "This is a very good Chinese book";//再次更改chineseBook的BookDescription属性
dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库,由于TransactionScope事务范围的存在,所以DbContext.SaveChanges方法提交的SQL语句都存在于TransactionScope的事务当中

时,EF Core的日志如下所示:

=============================== EF Core log started ===============================
SaveChanges starting for \'FinanceDigitalToolContext\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
DetectChanges starting for \'FinanceDigitalToolContext\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Unchanged \'Book.BookDescription\' detected as changed and will be marked as modified. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see property values.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
An \'Book\' entity tracked by \'FinanceDigitalToolContext\' changed from \'Unchanged\' to \'Modified\'. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see key values.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
DetectChanges completed for \'FinanceDigitalToolContext\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executing DbCommand [Parameters=[@p1=\'?\' (DbType = Int32), @p0=\'?\' (Size = 50)], CommandType=\'Text\', CommandTimeout=\'30\']
SET NOCOUNT ON;
UPDATE [Book] SET [BookDescription] = @p0
WHERE [ID] = @p1;
SELECT @@ROWCOUNT;
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executed DbCommand (22ms) [Parameters=[@p1=\'?\' (DbType = Int32), @p0=\'?\' (Size = 50)], CommandType=\'Text\', CommandTimeout=\'30\']
SET NOCOUNT ON;
UPDATE [Book] SET [BookDescription] = @p0
WHERE [ID] = @p1;
SELECT @@ROWCOUNT;
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
A data reader was disposed.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
An \'Book\' entity tracked by \'FinanceDigitalToolContext\' changed from \'Modified\' to \'Unchanged\'. Consider using \'DbContextOptionsBuilder.EnableSensitiveDataLogging\' to see key values.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
SaveChanges completed for \'FinanceDigitalToolContext\' with 1 entities written to the database.
=============================== EF Core log finished ===============================

从日志中我们可以看出来在执行dbContext.SaveChanges方法时,EF Core在数据库中并没有开启新的数据库连接,而是沿用了上一个DbContext.SaveChanges方法开启的数据库连接来提交SQL语句到数据库。然后chineseBook这个Book实体的EntityState从Modified变为了Unchanged。

 

然后执行

    transactionScope.Complete();//提交TransactionScope事务范围中的SQL语句到数据库,数据库事务结束
}

提交TransactionScope的事务到数据库,此时数据库事务结束,TransactionScope的事务范围也结束,EF Core没有输出日志

 

然后执行

chineseBook = dbContext.Book.First(bookExpression);//重新获取BookName为Chinese的Book实体chineseBook

时,EF Core的日志如下所示:

=============================== EF Core log started ===============================
Executing DbCommand [Parameters=[], CommandType=\'Text\', CommandTimeout=\'30\']
SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]
FROM [Book] AS [b]
WHERE [b].[BookName] = N\'Chinese\'
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Executed DbCommand (24ms) [Parameters=[], CommandType=\'Text\', CommandTimeout=\'30\']
SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]
FROM [Book] AS [b]
WHERE [b].[BookName] = N\'Chinese\'
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
A data reader was disposed.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Closing connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================
=============================== EF Core log started ===============================
Closed connection to database \'FinanceDigitalTool\' on server \'CNGDCAAITSQL01\'.
=============================== EF Core log finished ===============================

从日志中我们可以看出来,dbContext.Book.First(bookExpression)在数据库中也没有开启新的数据库连接,而是继续沿用了第一个DbContext.SaveChanges方法开启的数据库连接,使用SQL语句做了查询,之后关闭了第一个DbContext.SaveChanges方法开启的数据库连接,所以可以看到第一个DbContext.SaveChanges方法开启的数据库连接,现在才被关闭,这和不使用事务时是完全不一样的。

 

总结下来,使用事务后的代码和日志发生的事情如下:

  • dbContext.Book.First(bookExpression)开启和关闭了一个数据库连接,查询BookName为Chinese的Book实体chineseBook
  • using (TransactionScope transactionScope = new TransactionScope(TransactionScopeOption.RequiresNew)){开启了TransactionScope事务范围,数据库事务开始
  • 第一个dbContext.SaveChanges()开启一个数据库连接,但是没有关闭数据库连接,更改chineseBook的BookDescription属性值"This is a Chinese book"到数据库
  • 第二个dbContext.SaveChanges()没有开启新的数据库连接,而是沿用了上一个DbContext.SaveChanges方法开启的数据库连接,更改chineseBook的BookDescription属性值"This is a very good Chinese book"到数据库
  • transactionScope.Complete()提交TransactionScope事务范围的数据库事务到数据库,数据库事务结束
  • }TransactionScope事务范围结束
  • dbContext.Book.First(bookExpression)没有开启新的数据库连接,而是沿用了第一个DbContext.SaveChanges方法开启的数据库连接,重新查询BookName为Chinese的Book实体chineseBook,最后关闭了第一个DbContext.SaveChanges方法开启的数据库连接。

所以综上所述DbContext这次一共只开启和关闭了两个数据库连接,并且第二个数据库连接执行了三次数据库操作(两次DbContext.SaveChanges更改数据,一次Book.First查询数据)才被关闭。

 

由此我们可以看到EF Core在处于事务中时,会优化底层开启和关闭数据库连接的机制,因为EF Core觉得两次DbContext.SaveChanges方法提交的SQL语句既然都在同一个事务中,所以就没有必要每次都开启和关闭一个数据库连接,而是沿用了第一次DbContext.SaveChanges方法开启的数据库连接,所以这和没有使用事务的时候是完全不一样的。

 

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