此查询等效于sql中的EXISTS

var menuEntityList = context.MenuEntity.Where(
 m => context.MenuEntity.Where(m =>
 m.Title == thisVariable).Any(d => d.MenuId == m.ParentId)
                ).ToList();

我获得了Query with Profiler

exec sp_executesql N'SELECT [m].[Id], [m].[MenuId], [m].[ParentId], [m].[Title]
FROM [MenuEntity] AS [m]
WHERE EXISTS (
    SELECT 1
    FROM [MenuEntity] AS [m0]
    WHERE [m0].[Title] = @__thisVariable_0 
    AND [m0].[MenuId] = [m].[ParentId])'
,N'@__thisVariable_0 nvarchar(4000)',@__thisVariable_0=N'Org'

在C#中合并两个LINQ查询

您可以在LINQ中使用Join。

代码示例：

using (var ctx = ContextFactory.CreateDbContext())
{
   menuEntityList = await (
        from m in ctx.MenuEntity
        where m.ParentId == ctx.MenuEntity
            .Where(x => x.Title == thisVariable)
            .Select(x => x.MenuId)
            .Single()
        select m
   ).ToListAsync();
}

然而，正如你所看到的，代码并没有提供巨大的优势，我猜这两个选项可能在几乎每一个Angular 都是一样的。

与the answer by @AztecCodes的语法略有不同，更像SQL中的IN

using (var ctx = ContextFactory.CreateDbContext())
{
   menuEntityList = await (
        from m in ctx.MenuEntity
        where ctx.MenuEntity
            .Where(x => x.Title == thisVariable)
            .Select(x => x.MenuId)
            .Contains(m.ParentId)
        select m
   ).ToListAsync();
}