我有两个表:Vehicles 和 Workers。
Vehicle(Id, Number)
Workers(Id, Name, ContractorVehicleNumber)
我想编写 lambda 查询以返回所有车辆和承包商车辆。像在 sql 中的东西:
SELECT Id, Number
FROM Vehicle
UNION
SELECT NULL, ContractorVehicleNumber
FROM Workers
这是我做的:
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;
}
但我得到一个异常(exception):
The entity or complex type 'XXXXXXXX' cannot be constructed in a LINQ to Entities query.
最佳答案
您不能在投影中构造映射实体类型。仅当您创建用于投影的新特殊类型时,您之前的示例才会起作用:
public class VehicleResult
{
public string Number { get; set; }
... // If you don't need more then one column you can use simple type instead of custom class
}
您的方法将如下所示:
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;
}
关于c# - Entity Framework 中的联盟,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/6483711/