使用AutoMapper在Entity Framework中嵌套查询

Question

The use case is as follows: a customer account only ever has one address, either shipping or billing. I need to merge this into one Address entity. On top of this the address lines are separate columns in the database but have to be a IEnumerable of string in the DTO. All the while this must support ProjectTo() because OData must be implemented. How can I accomplish this without any database changes? I can't touch it because of legacy applications.

The first code example works, while the second fails with: The nested query is not supported. Operation1='Case' Operation2='Collect' The nested query is not supported. Operation1='Case' Operation2='Collect' . Which is probably because it has to create sub entities. How can I get it to work? Is there any workaround (perhaps restructuring my entities)?

In this first example I add the mappings for the different address line columns to a List<string> . Then when calling .Include() Entity Framework knows exactly what to do and it works.

public void Main()
{
    Mapper.Initialize(cfg =>
    {
        cfg.CreateMap<ShippingAddress, DtoShippingAddress>
            .ForMember(dto => dto.AddressLines,
                entity => entity.MapFrom(source => new List<string>
                    {
                        source.AddressLine1,
                        source.AddressLine2,
                        source.AddressLine3
                    }));

        cfg.CreateMap<BillingAddress, DtoBillingAddress>
            .ForMember(dto => dto.AddressLines,
                entity => entity.MapFrom(source => new List<string>
                    {
                        source.AddressLine1,
                        source.AddressLine2,
                        source.AddressLine3
                    }));
    });
    Mapper.AssertConfigurationIsValid();
    var context = new ClientContext();
    var result = context.CustomerAccounts.Include(i => i.ShippingAddress).Include(i => i.BillingAddress).ProjectTo<DtoCustomerAccount>();//.Dump();
}

public class CustomerAccount
{
    public int Id { get; set; }

    public ShippingAddress ShippingAddress { get; set; }

    public BillingAddress BillingAddress { get; set; }
}

public class ShippingAddress
{
    public int Id { get; set; }

    public string AddressLine1 { get; set; }

    public string AddressLine2 { get; set; }

    public string AddressLine3 { get; set; }
}

public class BillingAddress
{
    public int Id { get; set; }

    public string AddressLine1 { get; set; }

    public string AddressLine2 { get; set; }

    public string AddressLine3 { get; set; }
}

public class DtoCustomerAccount
{
    public int Id { get; set; }

    public DtoShippingAddress ShippingAddress { get; set; }

    public DtoBillingAddress BillingAddress { get; set; }
}

public class DtoShippingAddress
{
    public int Id { get; set; }

    public List<string> AddressLines { get; set; }
}

public class DtoBillingAddress
{
    public int Id { get; set; }

    public List<string> AddressLines { get; set; }
}

public class Initializer : DropCreateDatabaseAlways<ClientContext>
{       
    protected override void Seed(ClientContext context)
    {
        context.CustomerAccounts.Add(new UserQuery.CustomerAccount {ECommercePublished=true,  Articles = new []{ new Article{IsDefault=true, NationId=1, ProductId=1}}});
    }
}

public class ClientContext : DbContext
{
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
    Database.Log = s=>Debug.WriteLine(s);
        Database.SetInitializer(new Initializer());
    }

    public DbSet<CustomerAccount> CustomerAccounts { get; set; }
}

The way I need it implemented, which fails:

//The nested query is not supported. Operation1='Case' Operation2='Collect'
public void Main()
{
    Mapper.Initialize(cfg =>
    {
        cfg.CreateMap<CustomerAccount, DtoCustomerAccount>
            .ForMember(dto => dto.Address,
                entity => entity.MapFrom(source =>
                    source.BillingAddress == null
                        ? new Address
                        {
                            Id = source.ShippingAddress.Id,
                            AddressLines = new [] // or new List<string>
                            {
                                source.ShippingAddress.AddressLine1,
                                source.ShippingAddress.AddressLine2,
                                source.ShippingAddress.AddressLine3
                            }
                        }
                        : new Address
                        {
                            Id = source.BillingAddress.Id,
                            AddressLines = new [] // or new List<string>
                            {
                                source.BillingAddress.AddressLine1,
                                source.BillingAddress.AddressLine2,
                                source.BillingAddress.AddressLine3
                            }
                        }));
    });
    Mapper.AssertConfigurationIsValid();
    var context = new ClientContext();
    var result = context.CustomerAccounts.ProjectTo<DtoCustomerAccount>();//.Dump();
}

public class CustomerAccount
{
    public int Id { get; set; }

    public ShippingAddress ShippingAddress { get; set; }

    public BillingAddress BillingAddress { get; set; }
}

public class ShippingAddress
{
    public int Id { get; set; }

    public string AddressLine1 { get; set; }

    public string AddressLine2 { get; set; }

    public string AddressLine3 { get; set; }
}

public class BillingAddress
{
    public int Id { get; set; }

    public string AddressLine1 { get; set; }

    public string AddressLine2 { get; set; }

    public string AddressLine3 { get; set; }
}

public class DtoCustomerAccount
{
    public int Id { get; set; }

    public DtoAddress Address { get; set; }
}

public class DtoAddress
{
    public int Id { get; set; }

    public List<string> AddressLines { get; set; }
}

public class Initializer : DropCreateDatabaseAlways<ClientContext>
{       
    protected override void Seed(ClientContext context)
    {
        context.CustomerAccounts.Add(new UserQuery.CustomerAccount {ECommercePublished=true,  Articles = new []{ new Article{IsDefault=true, NationId=1, ProductId=1}}});
    }
}

public class ClientContext : DbContext
{
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
    Database.Log = s=>Debug.WriteLine(s);
        Database.SetInitializer(new Initializer());
    }

    public DbSet<CustomerAccount> CustomerAccounts { get; set; }
}

Answer 1

Technically it's not an AutoMapper issue, because ProjectTo simply uses the expression provided by you. And in this case the EF query trick with List<string> doesn't work with the conditional operator because BillingAddress and ShippingAddress are navigation properties and EF translator is trying to use sub queries which cannot be combined with conditional operator. Hence you need to find EF query compatible way of specifying the desired projection.

One possible way is to use conditional operator for each resultant address property:

.ForMember(dto => dto.Address, entity => entity.MapFrom(source => new DtoAddress
{
    Id = source.BillingAddress != null ? source.BillingAddress.Id : source.ShippingAddress.Id,
    AddressLines = new List<string>
    {
        source.BillingAddress != null ? source.BillingAddress.AddressLine1 : source.ShippingAddress.AddressLine1,
        source.BillingAddress != null ? source.BillingAddress.AddressLine2 : source.ShippingAddress.AddressLine2,
        source.BillingAddress != null ? source.BillingAddress.AddressLine3 : source.ShippingAddress.AddressLine3,
    }   
}))