LINQ表达式来匹配多个批量投入 [英] LINQ expression that will match multiple bulk inputs

问题描述

我怎么能写一个LINQ表达式来匹配多个批量投入？

这是我的数据库表

 会员
部，系
 1 3 
 4月9日* 
 5 1 
 6 3 * 
 9 2 
  

我要选择成员标有*

下面是我输入

  INT [] =师新INT [2] {4,6}; 
 INT [] =部门新INT [2] {9,3}; 
  

下面是我试过

<$ P $查询p> VAR selectedMembers = members.Where（成员=> divisions.Contains（member.Division）及和放大器; department.Contains（member.Department））。ToArray的（）;


这不正确的行为EF。它与一个单一的输入，但不能同时输入（司和处）
应该返回对在输入
如匹配时：

 会员[] = selectedMembers新成员国[2] {新会员司{= 4，系= 9}，新会员司{= 6系= 3}}; 
  

解决方案

此类型的过滤不直接由EF支持。

一个可能的解决方案是动态地建立这样一个判断：

 成员=> （member.Division ==区划[0]&放大器;&放大器; member.Department ==部门[0]）
 || （member.Division ==区划[1]安培;&安培; member.Department ==部门[1]）$ ​​B $ B ... 
 || （member.Division ==区划[N-1]&放大器;&放大器; member.Department ==部门[N-1]）; 
  

下面是你如何做到这一点：

 变量参数= Expression.Parameter（typeof运算（会员），会员）; 
 VAR谓词= Expression.Lambda< Func键<会员，布尔>>（
 Enumerable.Range（0，divisions.Length）
。选择（I =>新建表达式[] 
 {
 Expression.Equal（Expression.Property（参数司），Expression.Constant（师[I]）），
 Expression.Equal（Expression.Property（参数处），Expression.Constant（部门由[i]）），
} 
 .Aggregate（Expression.AndAlso））
 .Aggregate（Expression.OrElse），
参数）; 
 VAR的查询= members.Where（谓语）; 
  

How can I write a LINQ expression that will match multiple bulk inputs?

This is my database table

Members
Division, Department
1           3
4           9       *
5           1
6           3       *
9           2

I want to select the members marked with a *

Here are my inputs

int[] divisions = new int[2] {4, 6};
int[] department = new int[2] {9, 3};

Here's the query I tried

var selectedMembers = members.Where(member => divisions.Contains(member.Division) && department.Contains(member.Department)).ToArray();

This does not behave correctly in EF. It works when with a single input but not both inputs (Division and Department) It should return pairs matching in the inputs eg:

Member[] selectedMembers = new Member[2] { new Member{Division=4,Department=9}, new Member{Division=6,Department=3}};

解决方案

This type of filtering is not supported directly by EF.

One possible solution is to build dynamically a predicate like this:

member => (member.Division == divisions[0] && member.Department == departments[0])
       || (member.Division == divisions[1] && member.Department == departments[1])
       ...
       || (member.Division == divisions[N-1] && member.Department == departments[N-1]);

Here is how you can do that:

var parameter = Expression.Parameter(typeof(Member), "member");
var predicate = Expression.Lambda<Func<Member, bool>>(
    Enumerable.Range(0, divisions.Length)
    .Select(i => new Expression[]
    {
        Expression.Equal(Expression.Property(parameter, "Division"), Expression.Constant(divisions[i])),
        Expression.Equal(Expression.Property(parameter, "Department"), Expression.Constant(departments[i])),
    }
    .Aggregate(Expression.AndAlso))
    .Aggregate(Expression.OrElse),
    parameter);
var query = members.Where(predicate);

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