来自运行时数据层的 C# 中的动态 odata 服务

Posted 2023-03-09

【中文标题】来自运行时数据层的 C# 中的动态 odata 服务

【英文标题】：Dynamic odata service in C# from runtime data layer

【发布时间】：2015-07-10 23:50:56

【问题描述】：

我正在尝试从我的表中的表创建动态 odata 服务，这些表直到运行时才知道。因此，在我的 Web 应用程序启动时，用户选择了一个数据库，在 C# 中我找到了该数据库中的所有表。

现在最困难的部分是我想为数据库中的每个表创建 odata 服务端点，并在我的 Web 应用程序中相应地使用它们。问题是我不知道如何动态地做到这一点。有很多编译时已知数据库表的示例，但在这种情况下，直到我的用户第一次使用我的应用程序时我才会拥有它们。

【问题讨论】：

你有没有看odata.org/blog/…我也遇到了同样的情况，正在寻找这个问题的解决方案。

请澄清：您是说在服务初始化时让 OData 服务发现一组数据库和表吗？或者 OData 服务是否应该在其运行期间支持数据库的上下波动？

【参考方案1】：

这里有一个不需要预定义类的示例：ODataUntypedSample，但它确实需要预定义的控制器。

我在其上构建了另一个控制台应用程序示例，以便能够使用 OData 查询任何 SQL Server 数据库。我已经使用这个 nuget 包来读取数据库架构和数据：DatabaseSchemaReader。您需要以下 nuget 包才能构建它（加上依赖项）：

Microsoft.Owin.Hosting Microsoft.Owin.Host.HttpListener Microsoft.AspNet.WebApi.Owin Microsoft.AspNet.OData

这里是稍作修改的主程序，因此它从表中声明了 Edm（用于 OData）实体。我已经测试了标准样本Adventure Works 2014，但它应该适用于任何桌子：

class Program

    private static HttpClient client = new HttpClient();
    private static TableControllerSelector selector;
    private const string ServiceUrl = "http://localhost:12345";
    private const string connectionString = @"Server=mysqlSERVER;Database=AdventureWorks2014;Integrated Security=SSPI";

    static void Main(string[] args)
    
        using (WebApp.Start(ServiceUrl, Configuration))
        
            Console.WriteLine("Server is listening at 0", ServiceUrl);

            RunSample();

            Console.WriteLine("Press any key to continue . . .");
            Console.ReadKey();
        
    

    public static void Configuration(IAppBuilder builder)
    
        HttpConfiguration configuration = new HttpConfiguration();

        // create a special dynamic controller selector
        selector = new TableControllerSelector(configuration);
        IEdmModel  model = TableController.GetEdmModel(connectionString, selector);
        configuration.Services.Replace(typeof(IHttpControllerSelector), selector);

        configuration.MapODataServiceRoute("odata", "odata", model); // needs using System.Web.OData.Extensions
        builder.UseWebApi(configuration);
    

    public static void RunSample()
    
        Console.WriteLine("1. Get Metadata.");
        GetMetadata();

        Console.WriteLine("\n2. Get Entity Set.");
        using (var dbReader = new DatabaseReader(connectionString, "System.Data.SqlClient"))
        
            foreach (var table in dbReader.AllTables())
            
                Console.WriteLine("\n 2.1 Get Entity Set '" + table.Name  + "'.");
                GetEntitySet(table.Name);
            
        
    

    public static void GetMetadata()
    
        HttpResponseMessage response = client.GetAsync(ServiceUrl + "/odata/$metadata").Result;
        PrintResponse(response);
    

    public static void GetEntitySet(string tableName)
    
        HttpResponseMessage response = client.GetAsync(ServiceUrl + "/odata/" + tableName + "?$filter=Id eq 1").Result;
        PrintResponse(response);
    

    public static void PrintResponse(HttpResponseMessage response)
    
        response.EnsureSuccessStatusCode();
        Console.WriteLine("Response:");
        Console.WriteLine(response);

        if (response.Content != null)
        
            Console.WriteLine(response.Content.ReadAsStringAsync().Result);
        
    

还有特殊的 TableController 和 TableControllerSelector 类，它们允许从任何 SQL Server 数据库创建 Edm 模型，并从该模型中的 Edm 实体动态创建控制器：

public class TableControllerSelector : DefaultHttpControllerSelector

    private Dictionary<string, HttpControllerDescriptor> _tables = new Dictionary<string, HttpControllerDescriptor>(StringComparer.OrdinalIgnoreCase);

    public TableControllerSelector(HttpConfiguration configuration)
        : base(configuration)
    
        Configuration = configuration;
    

    public HttpConfiguration Configuration  get; private set; 

    public override HttpControllerDescriptor SelectController(HttpRequestMessage request)
    
        string name = GetControllerName(request);
        if (name != null) // is it a known table name?
        
            HttpControllerDescriptor desc;
            if (_tables.TryGetValue(name, out desc))
                return desc;
        

        return base.SelectController(request);
    

    public void AddTable(string connectionString, DatabaseTable table)
    
        if (connectionString == null)
            throw new ArgumentNullException("connectionString");

        if (table == null)
            throw new ArgumentNullException("table");

        // create a descriptor with extra properties that the controller needs
        var desc = new HttpControllerDescriptor(Configuration, table.Name, typeof(TableController));
        desc.Properties["table"] = table;
        desc.Properties["connectionString"] = connectionString;
        _tables[table.Name] = desc;
    


public class TableController : ODataController

    // this will be called for standard OData access to collection
    public EdmEntityObjectCollection Get()
    
        // get Edm type from request
        ODataPath path = Request.ODataProperties().Path; // ODataProperties() needs using System.Web.OData.Extensions
        IEdmType edmType = path.EdmType;

        IEdmCollectionType collectionType = (IEdmCollectionType)edmType;
        IEdmEntityType entityType = (IEdmEntityType)collectionType.ElementType.Definition;
        IEdmModel model = Request.ODataProperties().Model;

        ODataQueryContext queryContext = new ODataQueryContext(model, entityType, path);
        ODataQueryOptions queryOptions = new ODataQueryOptions(queryContext, Request);

        // TODO: apply the query option on the IQueryable here.

        // read all rows from table (could be optimized using query context)
        var table = (DatabaseTable)ControllerContext.ControllerDescriptor.Properties["table"];
        var cnx = (string)ControllerContext.ControllerDescriptor.Properties["connectionString"];

        return new EdmEntityObjectCollection(new EdmCollectionTypeReference(collectionType), ReadData(entityType, table, cnx));
    

    public static IList<IEdmEntityObject> ReadData(IEdmEntityType type, DatabaseTable table, string connectionString)
    
        List<IEdmEntityObject> list = new List<IEdmEntityObject>();

        // https://www.nuget.org/packages/DatabaseSchemaReader/
        Reader reader = new Reader(table, connectionString, "System.Data.SqlClient");
        reader.Read((r) =>
        
            EdmEntityObject obj = new EdmEntityObject(type);
            foreach (var prop in type.DeclaredProperties)
            
                int index = r.GetOrdinal(prop.Name);
                object value = r.GetValue(index);
                if (Convert.IsDBNull(value))
                
                    value = null;
                
                obj.TrySetPropertyValue(prop.Name, value);
            

            list.Add(obj);
            // uncomment these 2 lines if you're just testing maximum 10 rows on a table 
            //if (list.Count == 10)
            //    return false;

            return true;
        );
        return list;
    

    public static IEdmModel GetEdmModel(string connectionString, TableControllerSelector selector)
    
        EdmModel model = new EdmModel();

        // create and add entity container
        EdmEntityContainer container = new EdmEntityContainer("NS", "DefaultContainer");
        model.AddElement(container);

        // https://www.nuget.org/packages/DatabaseSchemaReader/
        using (var dbReader = new DatabaseReader(connectionString, "System.Data.SqlClient"))
        
            var schema = dbReader.ReadAll();
            foreach (var table in schema.Tables)
            
                EdmEntityType tableType = new EdmEntityType("NS", table.Name);
                foreach (var col in table.Columns)
                
                    var kind = GetKind(col);
                    if (!kind.HasValue) // don't map this
                        continue;

                    var prop = tableType.AddStructuralProperty(col.Name, kind.Value, col.Nullable);
                    if (col.IsPrimaryKey)
                    
                        tableType.AddKeys(prop);
                    
                
                model.AddElement(tableType);

                EdmEntitySet products = container.AddEntitySet(table.Name, tableType);
                selector.AddTable(connectionString, table);
            
        

        return model;
    

    // determine Edm kind from column type
    private static EdmPrimitiveTypeKind? GetKind(DatabaseColumn col)
    
        var dt = col.DataType;
        if (col.DataType == null)
            return null;

        Type type = col.DataType.GetNetType();
        if (type == null)
            return null;

        if (type == typeof(string))
            return EdmPrimitiveTypeKind.String;

        if (type == typeof(short))
            return EdmPrimitiveTypeKind.Int16;

        if (type == typeof(int))
            return EdmPrimitiveTypeKind.Int32;

        if (type == typeof(long))
            return EdmPrimitiveTypeKind.Int64;

        if (type == typeof(bool))
            return EdmPrimitiveTypeKind.Boolean;

        if (type == typeof(Guid))
            return EdmPrimitiveTypeKind.Guid;

        if (type == typeof(DateTime))
            return EdmPrimitiveTypeKind.DateTimeOffset;

        if (type == typeof(TimeSpan))
            return EdmPrimitiveTypeKind.Duration;

        if (type == typeof(decimal))
            return EdmPrimitiveTypeKind.Decimal;

        if (type == typeof(byte) || type == typeof(sbyte))
            return EdmPrimitiveTypeKind.Byte;

        if (type == typeof(byte[]))
            return EdmPrimitiveTypeKind.Binary;

        if (type == typeof(double))
            return EdmPrimitiveTypeKind.Double;

        if (type == typeof(float))
            return EdmPrimitiveTypeKind.Single;

        return null;
    

【讨论】：

感谢您提供此示例！快速说明 - 在最新版本中，要从请求中获取模型，您应该使用 IEdmModel model = Request.GetModel(); 而不是 IEdmModel model = Request.ODataProperties().Model;(in TableController.Get())

@GonçaloBorrêga - 是的 :-)，这也在我的评论中：github.com/OData/ODataSamples/issues/50#issuecomment-258799428

我们如何在表控制器上进行 OData 查询？喜欢Products?$filter=Name eq 'Milk' ?

【参考方案2】：

1.您是否尝试过使用字典？我不知道它是否适用于 OData，这只是一个想法，因为我使用过的各种数据连接/反序列化器也适用于字典。

2. 我更喜欢的想法是从数据源中检索一个类，我在这里找到了一些可能对您有帮助的东西：Class to DataSet / DataSet to class，也许如果没有更多障碍存在，使用返回的数据构建一个结构，将数据放入其中...

抱歉，我对答案有些不确定，只是想到了一些想法，我对 OData 知之甚少。希望对您有所帮助。