Insert records in multiple tables with same ID with Nhibernate hbm mapping

Question

I have two tables, Table 1 has a identity column(AttachmentID) and other fields, Table 2 has a AttachmentID column which is FK of Table1.AttachmentID and PK(not identity column), so Table1.AttachmentID = Table2.AttachmentID, records may or may not present in Table2 for all the records of Table1.

When I am saving records using Nhibernate entity classes, Records in table 1 and Table2 are being inserted correctly with the correct relationship but it also executing SCOPE_IDENTITY() after insert in table 2, since table 2 doesn't have any identity column so SCOPE_IDENTITY is giving null and because of this complete operation is being failed.

Following insert queries are being executed

exec sp_executesql N'INSERT INTO Table1 (FileName, GroupID, RelativeStorageLocation, FileSize, FileStatus, StorageTypeID, DocumentId, AccessKey, AttachmentSource, FileThumbnailID) VALUES (@p0, @p1, @p2, @p3, @p4, @p5, @p6, @p7, @p8, @p9); select SCOPE_IDENTITY()',N'@p0 nvarchar(4000),@p1 int,@p2 nvarchar(4000),@p3 bigint,@p4 int,@p5 int,@p6 int,@p7 nvarchar(4000),@p8 int,@p9 int',@p0=N'IMG_20180108_145645.jpg',@p1=52122,@p2=NULL,@p3=0,@p4=3,@p5=0,@p6=0,@p7=NULL,@p8=5,@p9=NULL    
exec sp_executesql N'INSERT INTO Table2 (DateTaken, ImageSource, ImageLocation, AttachmentID) VALUES (@p0, @p1, @p2, @p3); select SCOPE_IDENTITY()',N'@p0 datetime,@p1 nvarchar(4000),@p2 nvarchar(4000),@p3 int',@p0='2018-01-08 14:56:45',@p1=N'Xiaomi Redmi Note 4',@p2=N'Murzuq District, Libya',@p3=13045  

Following are the Nhibernate hbm files

Table 1(GenericAttachment)

<id name="_id" column="AttachmentID" access="field">
  <generator class="identity"/>
</id>

<property name="FileName" update="false"/>
<property name="GroupID"/>
<many-to-one name="GenericAttachmentGroup" class="GenericAttachmentGroup" column="GroupID" fetch="select" cascade="none" not-null="false" update="false" insert="false"/>
<property name="RelativeStorageLocation"/>
<property name="FileSize"/>
<property name="FileStatus" />
<property name="StorageTypeID" column="StorageTypeID" />
<property name="DocumentId" not-null="false"/>
<property name="AccessKey" not-null="false"/>
<property name="AttachmentSource" column="AttachmentSource" />
<many-to-one name="Thumbnail" class="FileInformation" column="FileThumbnailID" fetch="select" cascade="save-update" not-null="false" not-found="ignore"/>
<one-to-one lazy="proxy" name="Metadata" class="GenericAttachmentMatadataDetails" fetch="select" cascade="save-update" outer-join="true"  property-ref="GenericAttachment" />

Table 2(GenericAttachmentMatadataDetails)

<id name="_id" column="AttachmentID" access="field">
  <generator class="native"/>
</id>
<property name="DateTaken" column="DateTaken" />
<property name="ImageSource" column="ImageSource" />
<property name="ImageLocation" column="ImageLocation" />
<many-to-one name="GenericAttachment" class="Guru.Business.Entities.GenericAttachment, Guru.Business"  column="AttachmentID"  fetch="select" lazy="proxy" />

I am using C# with SQL server 2012.

Thanks

Answer 1

Generator class "foreign" solved the problem, Updated mapping configuration

Table 1(GenericAttachment)

<id name="_id" column="AttachmentID" access="field">
  <generator class="identity"/>
</id>
<property name="FileName" update="false"/>
<property name="GroupID"/>
<many-to-one name="GenericAttachmentGroup" class="GenericAttachmentGroup" column="GroupID" fetch="select" cascade="none" not-null="false" update="false" insert="false"/>
<property name="RelativeStorageLocation"/>
<property name="FileSize"/>
<property name="FileStatus" />
<property name="StorageTypeID" column="StorageTypeID" />
<property name="DocumentId" not-null="false"/>
<property name="AccessKey" not-null="false"/>
<property name="AttachmentSource" column="AttachmentSource" />
<many-to-one name="Thumbnail" class="FileInformation" column="FileThumbnailID" fetch="select" cascade="save-update" not-null="false" not-found="ignore"/>
<one-to-one lazy="proxy" name="Metadata" class="GenericAttachmentMetadataDetails" fetch="select" cascade="save-update" outer-join="true" property-ref="GenericAttachment"/>

Table 2(GenericAttachmentMatadataDetails)

<id name="_id" column="AttachmentID" access="field">
  <generator class="foreign">
        <param name="property">GenericAttachment</param>
   </generator>
</id>
<property name="DateTaken" column="DateTaken" />
<property name="ImageSource" column="ImageSource" />
<property name="ImageLocation" column="ImageLocation" />
<many-to-one name="GenericAttachment" access="property" class="GenericAttachment" fetch="select" insert="false" update="false" cascade="none" column="AttachmentID" unique="true" />