Fluent nHibernate many-to-many mapping

Question

I am trying to create entity with two FK from tables Group and Person.

public class Person
{
    public virtual int p_id { get; set; }
    public virtual string name { get; set; }
    public virtual IList<Person> ppl { get; set; }
}

public class Group
{
    public virtual int g_id { get; set; }
    public virtual string name{ get; set;}
    public virtual IList<Group> groups { get; set; }
}

Many-to-many mapping:

HasManyToMany(x => x.ppl)
    .Table("gp")
    .ParentKeyColumn("g_id")
    .ChildKeyColumn("p_id");

HasManyToMany(x => x.groups)
     .Table("gp")
     .ParentKeyColumn("p_id")
     .ChildKeyColumn("g_id")
     .Inverse();

Problem is that both constrains in table gp are referencing on table person. Show create table command:

CREATE TABLE `gp` (
`g_id` int(11) NOT NULL,
`p_id` int(11) NOT NULL,
KEY `p_id` (`p_id`),
KEY `g_id` (`g_id`),
CONSTRAINT `FK4B9E89089BCCDC65` FOREIGN KEY (`g_id`) REFERENCES `person` (`p_id`),
CONSTRAINT `FK4B9E8908E34BCD9E` FOREIGN KEY (`p_id`) REFERENCES `person` (`p_id`)

Want to:

CREATE TABLE `gp` (
`g_id` int(11) NOT NULL,
`p_id` int(11) NOT NULL,
KEY `p_id` (`p_id`),
KEY `g_id` (`g_id`),
CONSTRAINT `FK4B9E89089BCCDC65` FOREIGN KEY (`g_id`) REFERENCES `group` (`g_id`),
CONSTRAINT `FK4B9E8908E34BCD9E` FOREIGN KEY (`p_id`) REFERENCES `person` (`p_id`)

I tried to delete Inverse() in group mapping and use it in person table but I got following exception: "The relationship has Inverse specified on both sides". Does anyone knows why are constraints referencing one table?

granadaCoder granadaCoder · Accepted Answer · 2014-04-22T17:16:48

I have this:

I do not have "Inverse".

You have (singular)

.ParentKeyColumn("p_id")
.ChildKeyColumn("g_id")

I have adding to the collection, maybe something to try.

    .ParentKeyColumns.Add("p_id")
    .ChildKeyColumns.Add("g_id")

            (and vice versa)

Here are my 2 mappings (unaltered from my world, where Employee(s) have ParkingArea(s) and vice versa)............

        /* the below is how to do it without a surogatekey on the link table */
        HasManyToMany<ParkingAreaNHEntity>(x => x.MyParkingAreas)
       .Table("EmployeeToParkingAreaLink")
            .ParentKeyColumns.Add("AbcEmployeeUUID", p => p.UniqueKey("Emp_ParkingArea_Unique").Index("IX_ABC123"))
            .ChildKeyColumns.Add("AbcParkingAreaUUID", p => p.UniqueKey("Emp_ParkingArea_Unique"))
            .Cascade.None()
            ;




        /* the below is how to do it without a surogatekey on the link table */
        HasManyToMany<EmployeeNHEntity>(x => x.MyEmployees)
       .Table("EmployeeToParkingAreaLink")
            .ParentKeyColumns.Add("AbcParkingAreaUUID", p => p.UniqueKey("Emp_ParkingArea_Unique").Index("IX_ABC123"))
            .ChildKeyColumns.Add("AbcEmployeeUUID", p => p.UniqueKey("Emp_ParkingArea_Unique"))
            .Cascade.None()
            ;

Fluent nHibernate many-to-many mapping

2 Answers