Question

I have just started implementing ISet‘s instead of IList‘s in my project as that better reflects the collection’s I have.

This has thrown up an odd error in the creation of one table. The error I’m getting is.

Cannot define PRIMARY KEY constraint on nullable column in table ‘UserAddressAssignments’.

I have a many to many relationship between users and addresses.

public class User : BaseEntity
{
    public virtual System.Guid UserGuid { get; set; }
    public virtual string UserName { get; set; }
    public virtual Company Company { get; set; }
    public virtual Iesi.Collections.Generic.ISet<Address> UserAddressAssignments { get; set; }
}

The SQL it is generating for the lookup column is causing the issue and is shown below. It is the UserId column being nullable which is causing the problem.

create table UserAddressAssignments (
    UserAddressAssignmentId INT not null,
   AddressId INT IDENTITY NOT NULL,
   UserId INT null,
   primary key (UserId, AddressId)
)

The odd part here is that I have an identical relationship between a company and addresses which works fine.

public class Company : BaseEntity
{
    public virtual System.Guid CompanyGuid { get; set; }
    public virtual string Name { get; set; }
    public virtual Iesi.Collections.Generic.ISet<Address> CompanyAddressAssignments { get; set; }
}

This create the correct SQL for the lookup table.

CREATE TABLE [dbo].[CompanyAddressAssignments](
    [CompanyId] [int] NOT NULL,
    [AddressId] [int] NOT NULL,
PRIMARY KEY CLUSTERED 
(
    [CompanyId] ASC,
    [AddressId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

With a clustered key with the correct not null attributes for the keys and no third ‘CompanyAddressAssignmentId’ column as with the users lookup column.

The mapping overrides for both the Company and the User are identical too.

public class CompanyMappingOverride : IAutoMappingOverride<Company>
{
        public void Override(FluentNHibernate.Automapping.AutoMapping<Company> mapping)
        {
            mapping.Map(x => x.Name);
            mapping.HasManyToMany(x => x.CompanyAddressAssignments).Table("CompanyAddressAssignments").Cascade.All();
        }
}

public class UserMappingOverride : IAutoMappingOverride<User>
{
    public void Override(FluentNHibernate.Automapping.AutoMapping<User> mapping)
    {
        mapping.References(x => x.Company).Cascade.All();
        mapping.HasManyToMany(x => x.UserAddressAssignments).Table("UserAddressAssignments").Cascade.All();
    }
}

Does anyone have any suggestions on why the two lookup tables look so different when as far as I can tell the structure and mappings of the classes are identical?

I have resorted to using an IList for user addresses now to work around the issue.

This issues this create sql.

CREATE TABLE [dbo].[CompanyAddressAssignments](
    [CompanyId] [int] NOT NULL,
    [AddressId] [int] NOT NULL,
PRIMARY KEY CLUSTERED 
(
    [CompanyId] ASC,
    [AddressId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

Any ideas on what could be causing this discrepancy?

NHibernate version is 3.2.0.4000.

Cheers

Steve

Answer 1

Right I’ve found out what the issue was.

The site I’m working on has had NHibernate added to it. In order to use the code first / schema generation approach I used an automated tool to convert the existing schema into classes which the schema could then be magically created from.

I used NHhibernate designer to auto-generated the classes and then cleaned up the entities to match our standards.

http://www.devart.com/entitydeveloper/nhibernate-designer.html

The error crept in as the tool generated a class for the lookup table. So the UserAddressAssignment has its own class in the system. When creating a many to many relationship this is not usually required. Having specified both a class for the many to many and ALSO in the mapping override given the name of a ManyToMany table NHibernate must have got confused (unsurprisingly).

I would like to point out that the schema that NHibernate Designer had to work with was not all that clean any some of the relationships where not enforced, so I am not blaming it for creating this entity when not required!

So when I removed the unnecessary UserAddressAssignment class given below everything worked as expected.

  public class UserAddressAssignment : BaseEntity
    {
        public virtual int AddressId { get; set; }
        public virtual User User { get; set; }
        public virtual Address Address { get; set; }
    }

Hope this helps some one!

Cheers

Steve