Nhibernate一对多导致插入问题

Question

I'm trying to add new cross-reference tables to relate Accounts to Packages, and coming across a strange problem when I try to save the Account.

This cross-reference table has attributes of its own, so that's why I used a collection of them instead of Packages.

What happens is when I call SaveOrUpdate on the Account, NHibernate apparently decides to try to fill in other Account properties (like Product) with null objects. I've verified that commenting out the new mapping no longer causes the Product setter to get hit. (It also hits the other many-to-one mapped objects, it's nothing special about Product, that's just one example).

It's also important to note that this happens on insert only. On both update and insert, we'll set the ProductFk from some form input. On update Account.Product is already set by retrieving the Account from the database. On insert, a new Account is created where ProductFk is set but not Product. I suspect it's something about the Product being null causes NHibernate to try to fill it in before insert, but don't understand why adding this new mapping triggers that.

Here's my Account mapping file:

 <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="kpa.mko.dal" namespace="kpa.mko.dal.Entities.Accounts">
<class name="Account" table="Accounts">
    <id name="AccountId" type="Int32" unsaved-value="0">
        <generator class="identity" />
    </id>
    <property name="ParentAccountFk" />
    <many-to-one name="ParentAccount" column="ParentAccountFk" insert="false" update="false" />

    <property name="ProductFk" not-null="true" />
    <many-to-one name="Product" column="ProductFk" insert="false" update="false" />
    <property name="DistrictFk" not-null="true" />
    <many-to-one name="District" column="DistrictFk" insert="false" update="false" />
    <property name="Address1" />
    <snipped out other plain properties like Address1 />
    <set name="AccountPackageXrefs" table="Account_Package_xref" inverse="true">
        <key column="AccountFk"/>
        <one-to-many class="Account_Package_xref" />
    </set>
    <sql-insert>
        exec up_gen_Account_Insert @ParentAccountFk = ?, @ExternalAccountId = ?, @ClientAccountNumber = ?, @AccountName = ?
        ,@LogoFk = ?, @AccountTypeFk = ?, @AccountStatusFk = ?, @IsBillableAccount = ?, @ProductFk = ?, @HotLinkAccount = ?
        ,@FormGroupFk = ?, @DistrictFk = ?, @PrimaryEngineerFk = ?, @SecondaryEngineerFk = ?
        ,@Address1 = ?,@Address2 = ?,@City = ?,@StateFk = ?,@Zip = ?,@Country = ?,@Phone = ?,@Fax = ?,@TollFreeNumber = ?
        ,@BillingAddress1 = ?,@BillingAddress2 = ?,@BillingCity = ?,@BillingStateFk = ?,@BillingZip = ?,@BillingCountry = ?
        ,@BillingContactName = ?,@BillingContactPhone = ?,@BillingContactEmail = ?
        ,@TermDate = ?,@VisitValue = ?, @AccountIndustryTypeFk = ?, @CreatedByFk = ?,@CreatedDate = ?,@ModifiedByFk = ?,@ModifiedDate = ?
    </sql-insert>
</class>

and my Account_Package_xref mapping:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="kpa.mko.dal" namespace="kpa.mko.dal.Entities.Accounts">
<class name="Account_Package_xref" table="Account_Package_xref">
    <id name="AccountPackageId" type="Int32" unsaved-value="0">
        <generator class="identity" />
    </id>
    <property name="AccountFk"/>
    <property name="PackageFk"/>
    <property name="PrimaryConsultantFk"/>
    <property name="SecondaryConsultantFk" />
    <property name="CreatedById" column="CreatedByFk" not-null="true" update="false" />
    <property name="CreatedDate" not-null="true" update="false" />
    <property name="ModifiedById" column="ModifiedByFk" not-null="true" />
    <property name="ModifiedDate" not-null="true" />

    <many-to-one name="Account" column="AccountFk" not-null="true" insert="false" update="false"/>
    <many-to-one name="Package" column="PackageFk" not-null="true" insert="false" update="false"/>
</class>
<sql-query name="Account_Pacakge_xref_GetForAccountAndPackage">
    <return class="Account_Package_xref"/>
    exec Account_Package_xref_GetForAccountAndPackage @accountId = :accountId, @packageId = :packageId
</sql-query>

So when I execute this on insert

NHibernateSession.SaveOrUpdate(entity);

I see breakpoints hit in the setter here in Account, with a null value (which, of course, fails.)

public virtual ServicesProduct Product
{
    get { return _product; }
    set { 
        _product = value;
        ProductFk = value.ProductId;
    }
}

But only when I have the new mapping included. So, it's something about trying to add this new collection which I really don't understand.

I could probably add setting the Product in addition to the ProductFk when I construct a new Account, but that's a workaround and doesn't explain why adding this new relationship causes the system to act differently with respect to the Product (and like properties) of Account.

Answer 1

The point in ORM world is (ok, maybe just NHibernate) that

• assignment of ValueType (string including) is treated AS IS. It is not later re-checked (re-evaluated, re-assigned) again, when the original source of that value has changed
• assigning of ReferenceType is different. Reference ( Product ) assigned to property represents C# reference. At that moment the Product_ID was not resolved and was not assigned. So, NHibernate could wait for the ISession.Flush() and properly order all INSERT statements - as required.
  • Firstly Product is inserted...
  • its Product_ID is retrieved...
  • and could be used for INSERT of the root entity - as the Product_ID value

To make that all working we just have to change this mapping

// not the right way with ORM
<property name="ProductFk" not-null="true" />
<many-to-one name="Product" column="ProductFk" insert="false" update="false" />
<property name="DistrictFk" not-null="true" />
<many-to-one name="District" column="DistrictFk" insert="false" update="false" />

which is about ValueType being managed by NHiberante, into Reference management:

// object relations are mapped. That is ORM
<property name="ProductFk" not-null="true" insert="false" update="false" />
<many-to-one name="Product" column="ProductFk" />
<property name="DistrictFk" not-null="true" insert="false" update="false" />
<many-to-one name="District" column="DistrictFk" />

Also, because there are some magic sql-insert with some store procedures (are you still forced by some DB guy to do that?, no way how to avoid it?) , I would suggest to adjust the entity mapping like this

// fields
Product _product;

// properties
public virtual int ProductFk { get; set; }
public virtual Product Product
{
    get { return _product; }
    set
    {
        _product = value;
        ProductFk = _product != null ? _product.ProductId : 0;
    }
}