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问题描述

我不知道是否有人知道确切如果LINQ到SQL具有生成TSQL代码包含 ISNULL 函数的能力?



我知道,使用聚结操作符( ?? )中的查询:



邻表
,其中(o.Field ?? 0)GT; 0
选择o



将导致LINQ to SQL来发出 COALESCE 功能:



SELECT [T0] [现场]
从[表] AS [T0]
WHERE(COALESCE([T0] [现场],0))> 0

和,在使用条件运算符():



邻表
,其中(邻点域== NULL?0:o.Field)GT; 0
选择o



将导致TSQL包含 CASE 语句:



SELECT [T0] [现场]
从[表] AS [T0]
WHERE(
(CASE
当[T0]。[现场]为null,则0
ELSE [T0]。[金额]
端))> 0



不过,可以LINQ到SQL裹挟到包含生成TSQL代码 ISNULL 像下面这样?



SELECT [T0]。[现场]
FROM [表] AS [T0 [
,其中(ISNULL([T0] [技术领域],0)。)> 0



我打赌的回答是不,这不可能,但我会。喜欢看一些权威


解决方案

我知道实现这个是通过你自己的类,像这样的唯一方法:

 公共部分类LocalTestDataContext 
{
[功能(NAME =ISNULL,IsComposable = TRUE)]
[返回:参数(的DbType =的NVarChar(MAX))]
公共字符串ISNULL(
[参数(名称=场,的DbType =的NVarChar(MAX))]串场,
[参数(名称=输出的DbType =的NVarChar(MAX))]字符串输出)
{
回报率((字符串)(this.ExecuteMethodCall(这一点,
((MethodInfo的)(MethodInfo.GetCurrentMethod())),
场,输出).ReturnValue));
}
}

这是拿#3从此处

  VAR CTX =新LocalTest.LocalTestDataContext(); 

VAR的查询=从C在ctx.Categories
排序依据ctx.IsNull(c.Description1,)+ ctx.IsNull(c.Description2,)
选择C;
query.Dump();

和将产生的T-SQL中使用ISNULL()。


I was wondering whether anyone knows definitively if LINQ to SQL has the capability of generating TSQL code that contains the ISNULL function?

I'm aware that using the coalesce operator (??) in a query:

from o in Table
where (o.Field ?? 0) > 0
select o

will cause LINQ to SQL to emit the COALESCE function:

SELECT [t0].[Field]
FROM [Table] AS [t0]
WHERE (COALESCE([t0].[Field],0)) > 0

And, that using the conditional operator (?:) in a query:

from o in Table
where (o.Field == null ? 0 : o.Field) > 0
select o

will result in TSQL containing a CASE statement:

SELECT [t0].[Field]
FROM [Table] AS [t0]
WHERE (
    (CASE
        WHEN [t0].[Field] IS NULL THEN 0
        ELSE [t0].[Amount]
     END)) > 0

But, can LINQ to SQL be coerced into generating TSQL code that contains ISNULL like the following?

SELECT [t0].[Field]
FROM [Table] AS [t0]
WHERE (ISNULL([t0].[Field],0)) > 0

I'm betting the answer is "no, it can't," but I'd like to see something authoritative.

解决方案

The only way I know of accomplishing this is via your own class like so:

public partial class LocalTestDataContext
{
    [Function(Name = "IsNull", IsComposable = true)]
    [return: Parameter(DbType = "NVarChar(MAX)")]
    public string IsNull(
        [Parameter(Name = "field", DbType = "NVarChar(MAX)")] string field,
        [Parameter(Name = "output", DbType = "NVarChar(MAX)")] string output)
    {
        return ((string)(this.ExecuteMethodCall(this,
                ((MethodInfo)(MethodInfo.GetCurrentMethod())),
                field, output).ReturnValue));
    }
}

This is under "Take #3" from here.

var ctx = new LocalTest.LocalTestDataContext(); 

var query = from c in ctx.Categories 
orderby ctx.IsNull(c.Description1, "") + ctx.IsNull(c.Description2, "") 
select c; 
query.Dump();

And will generate T-SQL with ISNULL().

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10-14 23:23