我可以在Entity Framework中合并来自多个数据库的对象吗？

Question

I'm trying to figure out what the best way to tackle this would be. I have a Customer table in two different databases (not ideal I know, but it cannot be modified, I have to work with what I've been given). The records are kept in synch and share several fields (eg CustomerId, CustomerName, etc). But they also each have their own unique fields...so for example:

Database1 Customer

• CustomerId
• CustomerName
• Field1
• Field2

Database2 Customer

• CustomerId
• CustomerName
• DifferentField1
• DifferntField2

Each database has its own dbContext that I can independently pull each Customer object from. But what I would really like to have is a single unified Customer object that includes the union of all the fields in both dbs.

What would be the best way to accomplish this so that I can expose a single unified object?

EDIT: I am using DbSet and specifying a mapping for each entity in my context object, like this:

public DbSet<Customer> Customers { get; set; }

and then my mapping class has the typical mapping information:

this.ToTable("Customer");
this.HasKey(t => t.CustomerId);
this.Property(t => t.CustomerName);

etc. so I'm looking for a way to extend this logic with multiple tables/databases and be able to perform not just the queries but all the necessary CRUD operations

thanks

Answer 1

All you need to do is to declare a class which will represent an unified object:

public class UnifiedCustomer
{
    public int CustomerId {get; set;}
    public string Name {get; set;}
    public int Field1 {get; set;}
    public int Field2 {get; set;}
    public int DifferentField1 {get; set;}
    public int DifferentField2 {get; set;}
}

This type will be used to represent data from both databases:

var customers1 = dataContext1.Customers.Select(c => new UnifiedCustomer
{
    CustomerId = c.CustomerId,
    Name = c.CustomerName,
    Field1 = c.Field1,
    Field2 = c.Field2
});
var cusomers2 = dataContext2.Customers.Select(c => new UnifiedCustomer
{
    CustomerId = c.CustomerId,
    Name = c.CustomerName,
    DifferentField1 = c.DifferentField1,
    DifferentField2 = c.DifferentField2
});

Having both collections of the same type you can perform union:

var all = customers1.Union(customers2);

Answer 2

What would be the best way to accomplish this so that I can expose a single unified object?

You'll likely need to pull in the appropriate results from each context, then use LINQ to Objects to perform the "union" on the result sets in memory.

Answer 3

If two database are mapped to same class you can simple do:

        using (var cx1 = new customerEntities(firstDbConnectionString))
        {
            using (var cx2 = new customerEntities(secondDbConnectionString))
            {
                return cx1.tCustomer.ToList().AddRange(cx2.tCustomer.ToList());
            }
        }