英文:
Nesting a LINQ query inside a where clause of another query
问题
我如何将下面两个查询合并为单个查询？
使用（var ctx = ContextFactory.CreateDbContext（））
{
int parentId = await ctx.MenuEntity.Where(m => m.Title == thisVariable).Select(m => m.MenuId).SingleAsync();
menuEntityList = await ctx.MenuEntity.Where(m => m.ParentId == parentId).ToListAsync();
}
英文:
How would I combine the following two queries into a single query?
using (var ctx = ContextFactory.CreateDbContext())
{
int parentId = await ctx.MenuEntity.Where(m => m.Title == thisVariable).Select(m => m.MenuId).SingleAsync();
menuEntityList = await ctx.MenuEntity.Where(m => m.ParentId == parentId).ToListAsync();
}
答案1
得分: 1
你可以使用 LINQ 中的 Join 来实现。
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，这段代码并没有提供很大的优势，我猜在几乎每个方面两种选项可能都差不多。
英文:
Combine two LINQ queries in C#
You can do it by using Join in LINQ.
Code Example:
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();
}
However as you can see the code does not provide a huge advantage and I guess both options probably same in almost every perspective.
答案2
得分: 1
使用稍微不同的语法，更像是 SQL 中的 `IN` 语句：
```cs
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();
}
英文:
A slightly different syntax from the answer by @AztecCodes, more like an IN in SQL
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();
}
答案3
得分: 1
这个查询等同于SQL中的EXISTS。
var menuEntityList = context.MenuEntity.Where(
m => context.MenuEntity.Where(m =>
m.Title == thisVariable).Any(d => d.MenuId == m.ParentId)
).ToList();
我使用Profiler获得了查询结果。
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'
注意：上面的内容已经被我翻译了，不包含其他信息。
英文:
This query is equivalent to EXISTS in sql
var menuEntityList = context.MenuEntity.Where(
m => context.MenuEntity.Where(m =>
m.Title == thisVariable).Any(d => d.MenuId == m.ParentId)
).ToList();
I get 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'
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