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.

Answer 1

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

1. 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 ... } 

2. 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") ... } 

3. 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 )"); }