Create object containing a list using Dynamic Linq Core with Entity Framework 2.0

Question

I have the following two classes:

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;}
}

Using Entity Framework Core 2.0 I have associated these using a one to many relationship. Using Dynamic Linq Core I'm trying to create a query that returns the PartNumber, Description, and the list of all associated Warehouses for a particular part where the only property in the Warehouses list is WarehouseName ideally like this:

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();

But I receive this error: "No property or field 'Warehouse' exists in type 'List`1'". If I do something like this it works fine:

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();

The problem is that I would like it to be dynamic so that the user can just pass in a list of fields from the Part and Warehouse class that they want to get without having to modify the select to build it for those specific fields.

Try this as a test in your `fields`: `Warehouses[0].WarehouseName`. If that works then, you need to add the index for the other ones too. — CodingYoshi, Apr 13 '18 at 19:39
@CodingYoshi This returns a valid data object, but the WarehouseName is only a single field it isn't a list. How would I add the index to return all warehouses (there could be 0 to 100)? — jpico, Apr 13 '18 at 19:44

score 0 · Answer 1 · answered Aug 22 '19 at 08:16

You'd need to support a subquery on Warehouses. I'll copy the relevant steps listed in this answer:

add the following in ParseAggregate:

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

   ...
}

Add Select and ToList into IEnumerableSignatures, and a respective condition in ParseAggregate:

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")
   ...
}

Finally, Your query would be:

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
        )");
}

Create object containing a list using Dynamic Linq Core with Entity Framework 2.0

1 Answers1