你如何在 Linq 中写一个带有“OR”的 INNER JOIN

Posted 2023-03-23

【中文标题】你如何在 Linq 中写一个带有“OR”的 INNER JOIN

【英文标题】：How do you write an INNER JOIN with an "OR" in Linq

【发布时间】：2021-09-16 23:57:36

【问题描述】：

我正在尝试编写一个 Linq 查询来生成以下 SQL

SELECT 
    [t1].[Id], [t2].[value3]
FROM 
    [Table1] AS [t1]
INNER JOIN 
    [Table2] AS [t2] ON [t1].[Id] = [t2].[value1]
                     OR [t1].[Id] = [t2].[value2]

我已经看过很多关于如何进行多重连接的示例，但没有看到如何进行这种“一个或另一个”连接的示例。

【问题讨论】：

也许我的SQL to LINQ Recipe 可以帮助你。

【参考方案1】：

var result = from t1 in context.Table1
             from t2 in context.Table2
             where (t1.Id == t2.value1 || t1.Id == t2.value2)
             select new 
                     
                        t1.Id,
                        t2.value3
                    ;

【参考方案2】：

内连接

var query = 
    from t1 in context.Table1
    from t2 in context.Table2.Where(t2 => t1.Id == t2.value1 || t1.Id == t2.value2)
    select new 
     
        t1.Id,
        t2.value3
    ;

左连接

var query = 
    from t1 in context.Table1
    from t2 in context.Table2.Where(t2 => t1.Id == t2.value1 || t1.Id == t2.value2)
       .DefaultIfEmpty()
    select new 
     
        t1.Id,
        t2.value3
    ;