Fetch data from other table using fergin key using Entity Framework - entity-framework

Question

I have stuck with a problem where I can't get access to releted objects.
Table Customers
CustomerId | CurrencyId | AreaId
4 | 1 | 4
Table CustomersToArea
CustomerAreaId | AreaId
1 | 4
And what I'm trying to do is to get CurrencyId using AreaId as a key From table CustomersToArea to Customers table:
public class Customer
{
public int CustomerId {get; set}
public int CurrencyId {get; set}
public int AreaId {get; set}
}
public class CustomersToArea
{
public int CustomersToAreaId {get; set}
//and here I'd like to have access to Customers
//and be able to get CurrencyId
//I', trying this way, but does not work:
public virtual Customer Customer {get; set;}
}
Actually I don't know how to tell to entity framework, that these both tables should be joined using AreaId.
I don't want any additional table, if this is not possible maybe any workaround exists?

Answer 1

The schema would indicate that an Area table would exist. I'm not too sure what the role of "CustomerToArea" would be given Customer already has an AreaId in it. Normally something like that would be a Many-to-Many joining table.
Based on the schema provided, and assuming there is an Area table: Map the relationships between Customer, Area, and CustomerToArea. For instance:
public class Customer
{
public int CustomerId {get; set;}
public int CurrencyId {get; set;} // If there is a currency entity, I'd recommend mapping it instead.
// ...
public virtual Area {get; set;}
}
public class Area
{
public int AreaId {get; set;}
// ...
public virtual ICollection<CustomerToArea> CustomerToAreas {get; set;} = new List<CustomerToArea>();
}
public class CustomerToArea
{
public int CustomerToAreaId {get; set;}
// ...
public virtual Area {get; set;}
}
public class CustomerConfiguration : EntityTypeConfiguration<Customer>
{
public CustomerConfiguration()
{
ToTable("Customers");
HasKey(x => x.CustomerId)
.Property(x => x.CustomerId)
.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
HasRequired(x => x.Area)
.WithMany()
.Map(x => x.MapKey("AreaId")); // Maps the FK on Customer without needing to declare it in the entity. If declared, use .HasForeignKey(x => x.AreaId)
}
}
public class AreaConfiguration : EntityTypeConfiguration<Area>
{
public AreaConfiguration()
{
ToTable("Areas");
HasKey(x => x.AreaId)
.Property(x => x.AreaId)
.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
HasMany(x => x.CustomerAreas)
.WithRequired(x => x.Area)
.Map(x =>x.MapKey("AreaId"); // Maps the FK on CustomerArea.
}
}
public class CustomerAreaConfiguration : EntityTypeConfiguration<CustomerArea>
{
public AreaConfiguration()
{
ToTable("CustomerAreas");
HasKey(x => x.CustomerAreaId)
.Property(x => x.CustomerAreaId)
.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
}
}
Then if you wanted to get Customer's CurrencyId by a CustomerAreaId...
int customerAreaId = 12;
var customers = dbContext.Customers
.Where(x => x.Area.CustomerAreas
.Any(a => a.CustomerAreaId == customerAreaId))
.Select(x => x.CurrencyId)
.ToList();
Alternatively, remove the CustomerToArea table and just call it "Area" with a PK on the AreaId. What you've outlined for a schema seems broken. If there is no Area table, and you see no point in adding it then my recommendation would be to fix the schema relations rather than break EF's relational mappings.