Nhibernate one to many relationship error

Question

I am encountering foreign key error while saving child record for parent-child relationship in nhibernate. I am using Mysql as the database. Value of foreign key column inserted is "0"

Table

CREATE TABLE Company(
   Id INT NOT NULL AUTO_INCREMENT,
   Name Varchar(100) NOT NULL,
   PRIMARY KEY (Id)
);

CREATE TABLE Client(
   ClientId INT NOT NULL AUTO_INCREMENT,
   CompanyId INT NOT NULL,
   Name Varchar(100) NOT NULL,
   PRIMARY KEY (ClientId),
   FOREIGN KEY(CompanyId) REFERENCES  Company(Id)
);

Class:

public class Company
{
    private IList<Client> clients = new List<Client>();

    public virtual IList<Client> Clients
    {
        get { return clients; }
        set { clients = value; }
    }

    public  virtual void AddClientToCompany(Client client)
    {
        client.Company = this; 
        clients.Add(client);
    }

    public virtual Company Company { get; set; }

    public virtual string Name { get; set; }

    public virtual int Id { get; set; }
}

public class Client
{
    public virtual Company Company { get; set; }

    public virtual string Name { get; set; }

    public virtual int CompanyId { get; set; }

    public virtual int ClientId { get; set; }   
}

 Company.hbm.xml
   <class name="ConsoleApplication1.Company, ConsoleApplication1"          table="Company">
      <id name="Id" column="Id" type="int">
       <generator class="native"></generator>
      </id>
      <property name="Name" column="Name" type="String"></property>

      <bag name="Clients" table="Client" lazy="false" cascade="all"     inverse="true">
       <key column="CompanyId"></key>
       <one-to-many class="ConsoleApplication1.Client, ConsoleApplication1"         />
   </bag>
  </class>

Client.hbm.xml

<class name="ConsoleApplication1.Client, ConsoleApplication1"   table="Client">
   <id name="ClientId" column="ClientId" type="int">
      <generator class="native"></generator>
    </id>
    <property name="Name" column="Name" type="String"></property>
    <property name="CompanyId" column="CompanyId" type="int" ></property>

    <many-to-one name="Company"  class="ConsoleApplication1.Company,    ConsoleApplication1" 
             column="CompanyId" cascade="none" insert="false"/>
 </class>

Sql generated:

NHibernate: INSERT INTO Company (Name) VALUES (?p0);?p0 = 'Test Company' [Type: String (12)] NHibernate: SELECT LAST_INSERT_ID()

NHibernate: INSERT INTO Client (Name, CompanyId) VALUES (?p0, ?p1);?p0 = 'Test Client' [Type: String (11)], ?p1 = 0 [Type: Int32 (0)]

Runtime code:

        Company company = new Company();
        company.Name = "Test Company";

        Client client = new Client();
        client.Name = "Test Client";

        company.AddClientToCompany(client);

        session.Save(company);

Any ideas what could be the issue?

Radim Köhler Radim Köhler · Accepted Answer · 2015-03-09T07:24:36

The point here is that for both many-to-one and one-to-many we have to use the same column "CompanyId"

The Company.hbm.xml

<bag name="Clients" table="Client" lazy="false" 
     cascade="all" inverse="true" >
  <!-- wrong column name, it must be parent reference in a child table -->
  <!-- <key column="ClientId"></key> -->
  <key column="CompanyId" />
  <one-to-many class="ConsoleApplication1.Client, ConsoleApplication1" />
</bag>

The Client.hbm.xml - the same column is used for the reversed mapping CompanyId

<many-to-one name="Company"  
             class="ConsoleApplication1.Company, ConsoleApplication1" 
             column="CompanyId" 
             cascade="none"/>

Really, there is exactly ONE column (CompanyId) which is responsible for both sides of the mapping... the same principal as a relation in DB

EXTEND:

Once we correct mapping, we MUST be sure, that we do set both sides of the relationship in C#. this is needed, because of inverse="true" mapping.

The best way is to extend the AddClientToCompany() to be assigning both sides:

public class Company
{
    ...
    public  virtual void AddClientToCompany(Client client)
    {
        clients.Add(client);
        // essential line
        client.Company = this;
    }
    ...

And the runtime code:

var client = new Client
{
   ...
}
var company = new Company
{
   ...
}
// no company knows about client 
// and client knows abtou company
company.AddClientToCompany(client);
session.Save(company);

NHibernate will now properly inject the INSERT with related entity ID...

After all that, what we have to really be sure about, is that the reference mapping is editable - not the property:

<property name="CompanyId" column="CompanyId" type="int"
      insert="false" update="false" >
// the above must be insert and update false
// the below must be editable - it is a reference - managed by NHibernate
<many-to-one name="Company"  
      class="ConsoleApplication1.Company,    ConsoleApplication1" 
      column="CompanyId" cascade="none"/>

Nhibernate one to many relationship error

1 Answers