联盟实体框架 [英] Union in entity framework

问题描述

我有两个表：车辆和工人。

 车辆（身份证，号码）
工人（ID，姓名，ContractorVehicleNumber）
 

我想写的lambda查询返回所有的车辆和承包车辆。喜欢的东西在SQL：

  SELECT身份证，号码
车用
联盟
SELECT NULL，ContractorVehicleNumber
工人
 

这是我做了什么：

 公开的IQueryable＆LT;车＆GT;获取（布尔includeContractorVehicles）
{
    IQueryable的＆LT;车＆GT;查询= GetQuery（）;

    如果（includeContractorVehicles ==真）
    {
        WorkerRepository代表=新WorkerRepository（）;
        IQueryable的＆LT;车＆GT; contractorsVehicles = rep.GetWirkers（）。
            选择（X =＆gt;新建汽车（）
            {
                VehicleNumber = x.ContractorVehicleNumber
            }）;
        查询= query.Union（contractorsVehicles）;
    }

    返回查询;
}
 

不过，我得到一个异常：

  

实体或复杂类型XXXXXXXX'不能在LINQ到实体查询构造。

解决方案

您不能构造投影映射的实体类型。如果您创建用于投影新的特殊类型的前例只会工作：

 公共类VehicleResult
{
    耻骨串号{获得;组; }
    ... //如果你不需要更多然后一栏，你可以使用简单的类型，而不是自定义类
}
 

和你的方法是这样的：

 公开的IQueryable＆LT; VehicleResult＆GT;获取（布尔includeContractorVehicles）
{
    IQueryable的＆LT; VehicleResult＆GT; 。查询= GetQuery（）选择（V =＆gt;新建VehicleResult {...}）;

    如果（includeContractorVehicles ==真）
    {
        WorkerRepository代表=新WorkerRepository（）;
        IQueryable的＆LT; VehicleResult＆GT; contractorsVehicles = rep.GetWorkers（）。
            选择（X =＆gt;新建VehicleResult（）
            {
                数= x.ContractorVehicleNumber
            }）;
        查询= query.Union（contractorsVehicles）;
    }

    返回查询;
}
 

I have two tables: Vehicles and Workers.

Vehicle(Id, Number)
Workers(Id, Name, ContractorVehicleNumber)

I would like to write lambda query to return all the vehicles and the contractor vehicles. Something like in sql:

SELECT Id, Number
FROM Vehicle
UNION
SELECT NULL, ContractorVehicleNumber
FROM Workers

This is what I made:

public IQueryable<Vehicle> Get(bool includeContractorVehicles)
{
    IQueryable<Vehicle> query = GetQuery();

    if (includeContractorVehicles == true)
    {
        WorkerRepository rep = new WorkerRepository();
        IQueryable<Vehicle> contractorsVehicles = rep.GetWirkers().
            Select(x => new Vehicle()
            {
                VehicleNumber = x.ContractorVehicleNumber
            });
        query = query.Union(contractorsVehicles);
    }

    return query;
}  

But I get an exception:

The entity or complex type 'XXXXXXXX' cannot be constructed in a LINQ to Entities query.

解决方案

You cannot construct mapped entity type in projection. Your former example will work only if you create a new special type used for projection:

public class VehicleResult
{
    pubic string Number { get; set; }
    ... // If you don't need more then one column you can use simple type instead of custom class
}

And your method will look like:

public IQueryable<VehicleResult> Get(bool includeContractorVehicles)
{
    IQueryable<VehicleResult> query = GetQuery().Select(v => new VehicleResult { ... });

    if (includeContractorVehicles == true)
    {
        WorkerRepository rep = new WorkerRepository();
        IQueryable<VehicleResult> contractorsVehicles = rep.GetWorkers().
            Select(x => new VehicleResult()
            {
                Number = x.ContractorVehicleNumber
            });
        query = query.Union(contractorsVehicles);
    }

    return query;
}  

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