DDD实体框架值类型

Question

I'm struggling with using EF6 with DDD principles, namely value objects attached to aggregates. I can't seem to get migrations to generate that reflect the model and I feel like I'm fighting the tooling instead of actually being productive. Given that a NoSQL implementation is probably more appropriate, this is what I'm stuck with.

The first thing that I ran into was the lack of support for interface properties on an EF entity. The work around for that was to add concrete properties to the entity for each of the implementations, but not to the interface. When I implemented the interface, I added logic to return the right one. I had to do this in order to get any migrations to create the properties for the Policies. See Fund.LargestBalanceFirstAllocationPolicy and Fund.PercentageBasedAllocationPolicy This was annoyance one.

The current annoyance and the genesis of the question is the PercentageBasedAllocationPolicy.AllocationValues property. No matter what I do, when running add-migration, I don't get any tables or fields to represent the AllocationValues. This is basically a collection of DDD value objects hanging off of another value object, which hangs off of an aggregate.

I'm convinced that the model and code are correct to do what I want, but EF keeps getting in the way. In MongoDB, when dealing with an interface property, it actually stores the object type in a string so that it knows how to rehydrate the object. I'm considering serializing the problem areas here to a blob and storing it on the object now, which is just as evil...

public interface IFund
{
    Guid Id {get;}
    string ProperName {get;}
    IAllocationPolicy AllocationPolicy{get;}
    void ChangeAllocationPolicy(IAllocationPolicy newAllocationPolicy)
}


public class Fund : IFund
{
    public Fund()
    {

    }

    public Fund(Guid id, string nickName, string properName)
    {
        Id = id;
        Nickname = nickName;
        ProperName = properName;

        // This is stupid too, but you have to instantiate these objects inorder to save or you get some EF errors.  Make sure the properties on these objects are all defaulted to null.
        LargestBalanceFirstAllocationPolicy = new LargestBalanceFirstAllocationPolicy();
        PercentageBasedAllocationPolicy = new PercentageBasedAllocationPolicy();

    }

    public Guid Id { get; private set; }

    public string ProperName { get; private set; }


    // Do not add this to the interface.  It's here for EF reasons only.  Do not use internally either.  Use the interface implemention of AllocationPolicy instead
    public LargestBalanceFirstAllocationPolicy LargestBalanceFirstAllocationPolicy
    {
        get; private set;
    }

    // Do not add this to the interface.  It's here for EF reasons only.  Do not use internally either.  Use the interface implemention of AllocationPolicy instead
    public PercentageBasedAllocationPolicy PercentageBasedAllocationPolicy
    {
        get; private set;
    }


    public void ChangeAllocationPolicy(IAllocationPolicy newAllocationPolicy)
    {
        if (newAllocationPolicy == null) throw new DomainException("Allocation policy is required");

        var allocationPolicy = newAllocationPolicy as PercentageBasedAllocationPolicy;
        if (allocationPolicy != null) PercentageBasedAllocationPolicy = allocationPolicy;

        var policy = newAllocationPolicy as LargestBalanceFirstAllocationPolicy;
        if (policy != null  ) LargestBalanceFirstAllocationPolicy = policy;
    }

    public IAllocationPolicy AllocationPolicy
    {
        get {

            if (LargestBalanceFirstAllocationPolicy != null)
                return LargestBalanceFirstAllocationPolicy;

            if (PercentageBasedAllocationPolicy != null)
                return PercentageBasedAllocationPolicy;

            return null;
        }

    }
}

public interface IAllocationPolicy
{
    T Accept<T>(IAllocationPolicyVisitor<T> allocationPolicyVisitor);
}

public class LargestBalanceFirstAllocationPolicy : IAllocationPolicy
{
    public T Accept<T>(IAllocationPolicyVisitor<T> allocationPolicyVisitor)
    {
        return allocationPolicyVisitor.Visit(this);
    }
}

[ComplexType]
public class PercentageBasedAllocationPolicy : IAllocationPolicy
{
    public PercentageBasedAllocationPolicy()
    {
        AllocationValues = new List<PercentageAllocationPolicyInfo>();
    }

    public List<PercentageAllocationPolicyInfo> AllocationValues { get; private set; }

    public T Accept<T>(IAllocationPolicyVisitor<T> allocationPolicyVisitor)
    {
        return allocationPolicyVisitor.Visit(this);
    }
}

[ComplexType]
public class PercentageAllocationPolicyInfo
{
    public Guid AssetId { get; private set; }

    public decimal Percentage { get; private set; }
}

Answer 1

A value type (in EF marked as ComplexType) will never have any tables. The reason being is that a value types are (by definition) really just values. They don't have any Id( otherwise they would be enities) thus you can't create a table for them.

also if i review the requirements for complex type in entity framework https://msdn.microsoft.com/en-us/library/bb738472(v=vs.100).aspx i notice that you can't use inheritance on complex types. Thus if you want to use complex type in your entity framework as you've shown here then you need to make your property a PercentageBasedAllocationPolicy instead of an IAllocationPolicy.

Alternatively you could turn it into an entity with automatic generated keys.