Question

我正在修改我的项目以使用DBContext而不是ObjectContext。我现有的代码

$yourArray = json_decode($yourJSON, true);
$yourFormattedArray = array();
$map = array(
    'true' => true,
    'false' => false
    // more as needed
);

foreach ($yourArray as $key => $val ) {
    if ( isset($map[$val]) ) {
        $val = $map[$val];
    }
    $yourFormattedArray[str_replace('_', '.', $key)] = $val;
}

$yourFinalArray = json_encode($yourFormattedArray);

上面的代码是使用ObjectContext编写的。将我的项目更改为继承自DBContext后，我收到以下错误

var query = context.Vehicles.OrderBy("it.VehicleType.VehicleTypeID").
            GroupBy("it.VehicleType.VehicleTypeID", "Min(it.ODO_Reading) AS MinRunVehicle, it.VehicleType.VehicleTypeID");

我想知道如何在DBContext中指定动态Linq查询。有人可以帮忙。

Answer 1

您可以使用

var query = context.Vehicles.OrderBy(m=>m.it.VehicleType.VehicleTypeID)

Answer 2

以下是如何转换所有内容，包括OrderBy和GroupBy

void Main()
{

    var vehicles = new List<Vehicle>();

    for (int i = 0; i < 10; i++)
    {
        vehicles.Add(new Vehicle());
    }

    vehicles.OrderBy(vehicle     => vehicle.VehicleType.VehicleTypeID)
            .GroupBy(vehicleType => vehicleType.VehicleType.VehicleTypeID, 
                     vehicle     => vehicle.ODO_Reading, 
                                    (vehicleTypeID, minRunVehicle) => new 
                                    {
                                        VehicleTypeId = vehicleTypeID, 
                                        minRunVehicle = minRunVehicle
                                    })
            .ToList()
            .ForEach(vehicle => 
                     {
                         Console.WriteLine(vehicle.VehicleTypeId);
                         vehicle.minRunVehicle.ToList()
                                              .ForEach(minRun =>
                                              {
                                                  Console.WriteLine ("\t > :" + minRun);
                                              });
                         Console.WriteLine ("\n");
                     });
}

public class Vehicle
{
    public Vehicle()
    {
        this.VehicleType = new VehicleType();
        this.ODO_Reading = random.Next(100, 100000);
    }

    public VehicleType VehicleType { get; set;  }
    public int ODO_Reading { get; set; }
}

public class VehicleType
{
    public VehicleType()
    {
        VehicleTypeID = random.Next(1, 10);
    }

    public int VehicleTypeID { get; set; }
} 

public static Random random = new Random();

Answer 3

第一个示例使用eSQL，而不是某种类型的动态LINQ。

DbContext不允许您直接执行eSQL查询，但您可以访问基础ObjectContext并像以前一样使用它：

var query = ((IObjectContextAdapter)context).ObjectContext
                                            .CreateQuery<Vehicle>("<ESQL Query>")

如何在C＃中使用DBContext编写动态LINQ查询

3 个答案: