如何重构多个类似的Linq-To-Sql查询? [英] How to refactor multiple similar Linq-To-Sql queries?

问题描述

在投票或关闭之前请阅读:这几乎是

Read before downvoting or closing: This almost exact duplicate of a previous question of mine exists with the solely purpose to rephrase the previous question to the Linq-To-Sql scope. All answers contained in the previous question are valid for the Linq scope, but are invalid in the Linq-To-SQL scope.

假设我要重构以下两个Linq-To-SQL查询:

Suppose I have the two following Linq-To-SQL queries I want to refactor:

var someValue1 = 0;
var someValue2= 0;
var query1 = db.TableAs.Where( a => a.TableBs.Count() > someValue1 )
              .Take( 10 );
var query2 = db.TableAs.Where( a => a.TableBs.First().item1 == someValue2)
              .Take( 10 );

请注意，只有Where参数会更改.有什么方法可以将查询放入方法中，并将Where参数作为参数传递?

Note that only the Where parameter changes. There is any way to put the query inside a method and pass the Where parameter as an argument?

已经尝试了上一个问题中发布的所有解决方案.尝试枚举结果时在运行时失败.

All the solutions posted in the previous question have been tried and failed in runtime when I try to enumerate the result.

抛出的异常是:查询运算符'Where'使用了不受支持的重载"

The exception thrown was: "Unsupported overload used for query operator 'Where'"

推荐答案

绝对.您会写:

public IQueryable<A> First10(Expression<Func<A,bool>> predicate)
{
    return db.TableAs.Where(predicate).Take(10);
}

(假设TableA是IQueryable<A>.)

致电:

var someValue1 = 0;
var someValue2= 0;
var query1 = First10(a => a.TableBs.Count() > someValue1);
var query2 = First10(a => a.TableBs.First().item1 == someValue2);

我相信会起作用的...

此方法与您上一个问题的答案之间的区别基本上是，此方法使用Expression<Func<T,bool>>而不是Func<T,bool>，因此最终使用Queryable.Where而不是Enumerable.Where.

The difference between this and the answers to your previous question is basically that this method takes Expression<Func<T,bool>> instead of just Func<T,bool> so it ends up using Queryable.Where instead of Enumerable.Where.

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