Question

我有以下两个类：

public Part {
    public string PartNumber {get; set;}
    public string Description {get; set;}
    public List<Warehouse> Warehouses {get; set;}
}

public Warehouse {
    public string PartNumber {get; set;}
    public string WarehouseName {get; set;}
    public int Quantity {get; set;}
    public int ReorderPoint {get; set;}
}

使用Entity Framework Core 2.0我使用一对多关系关联它们。使用Dynamic Linq Core我尝试创建一个查询，返回PartNumber，Description以及特定部分的所有相关仓库的列表，其中Warehouses列表中唯一的属性是WarehouseName，理想情况如下：

List<string> fields = new List<string> {"PartNumber", "Description", "Warehouses.WarehouseName"};
var _dataSet = dbContext.Parts.Include(x => x.Warehouses);
var data = _dataSet.Where("PartNumber = \"Part1234\"").Select("new (" + String.Join(",", fields) + ")").ToDynamicArray();

但是我收到了这个错误：＆＃34;没有财产或字段＆＃39;仓库＆＃39;存在于类型＆＃39; List`1＆＃39;＆＃34;中。如果我做这样的事情就可以了：

var data = _dataSet.Where("PartNumber = \"Part1234\"").Select(x => new Part
{
    PartNumber = x.PartNumber,
    Description = x.Description,
    Warehouses = x.Warehouses.Select(y => new Warehouse { Warehouse = y.Warehouse }).ToList()
}).Single();

问题在于我希望它是动态的，以便用户只需传入他们想要获得的Part和Warehouse类的字段列表，而无需修改select以为这些特定字段构建它

Answer 1

您需要在Warehouses上支持子查询。我将复制this answer中列出的相关步骤：

在ParseAggregate中添加以下内容：

Expression ParseAggregate(Expression instance, Type elementType, string methodName, int errorPos)
{
   // Change starts here
   var originalIt = it;
   var originalOuterIt = outerIt;
   // Change ends here

   outerIt = it;
   ParameterExpression innerIt = Expression.Parameter(elementType, elementType.Name);
   it = innerIt;
   Expression[] args = ParseArgumentList();

   // Change starts here
   it = originalIt;
   outerIt = originalOuterIt;
   // Change ends here

   ...
}

在Select中添加ToList和IEnumerableSignatures，并在ParseAggregate中添加相应的条件：

interface IEnumerableSignatures
{
  ...
  void Select(object selector);
  void ToList();
  ...
}

Expression ParseAggregate(Expression instance, Type elementType, string methodName, int errorPos)
{
   ...
   if (signature.Name == "Min" || 
       signature.Name == "Max" || 
       signature.Name == "Select")
   ...
}

最后，您的查询将是：

static void Main()
{
    // example data
    var warehouses = new List<Warehouse>
    {
        new Warehouse { WarehouseName = "NY1", Quantity = 10 },
        new Warehouse { WarehouseName = "NY2", Quantity = 100 }
    };
    var parts = new List<Part> 
    { 
         new Part { PartNumber = "1", Description = "Hammer", Warehouses = warehouses } 
    };
    // query
    var result =
        parts
        .Select(@"new ( 
           PartNumber,
           Description,
           Warehouses.Select(WarehouseName).ToList() as WarehouseNames
        )");
}

使用带有Entity Framework 2.0的Dynamic Linq Core创建包含列表的对象

1 个答案: