Many-to-many with Same Id Key fields

问题

How do I join two tables as many-to-one and one-to-many in nHibernate. They both have the same 'PLAN_ID' as the key column. My Database structures pre-existing.

Below is the mapping I am using and the error I'm getting:

Table: PLANN (one)

PLAN_ID  <-- PRIMARY KEY
START_DATE
CHECK_CHAR
...

Table: PLANN_DOCUMENT (to many)

PLAN_ID <-- PRIMARY KEY
DOC_ID <-- ID to a DOCUMENT table
DOC_NAME
DOC_TYPE

Plann class:

public virtual... PlanId, StartDate, CheckChar, PlanStatus,
public virtual ISet<DocsysHoldingDoc> DocsysHoldingDocs { get; set; }
public virtual DocsysHoldingDoc DocsysHoldingDoc { get; set; }

PlannDocument Class:

public virtual...PlanId, DocId, DocName, DocType
public virtual Plann PlannItem { get; set; }

Plann HBM XML

<class name="Plann" abstract="true" table="PLANN">
    <id name="PlanId" column="PLAN_ID"
        <generator class="assigned"/>
    </id>
    <property name="StartDate" column="START_DATE" /> 
    <property name="CHECK_CHAR" column="CHECK_CHAR" /> 
    ...

    <set name="PlannDocument" table="PLANN_DOCUMNET">
        <key column="PLAN_ID"></key> //<<KEY IN JOINING TABLE BUT ALSO ID IN THIS TABLE
        <one-to-many class="DocsysHoldingDoc"/>
     </set>
</class>

PlannDocument HBM XML

<class name="PlannDocument" abstract="true" table="PLANN_DOCUMNET">
    <id name="PlanId" column="PLAN_ID"  type = "int">
        <generator class="assigned"/>
    </id>
    <property name="DocId" column="DOC_ID" />
    <property name="DocName" column="DOC_NAME" />
    <property name="DocType" column="DOC_TYPE" />

    <many-to-one name="Plann" column="PLAN_ID"></many-to-one>

</class>

ERROR: NHibernate.MappingException: 'Unable to build the insert statement for class <>.PlannDocument: a failure occurred when adding the Id of the class'

ArgumentException: The column 'PLAN_ID' has already been added in this SQL builder Parameter name: columnName

Am I doing something wrong here?

回答1:

Based on your comments (under deleted answer), name of primary key column in both the tables is same - i.e. PLAN_ID. You want to join these two tables based on many-to-one relation.

The problem here is that the same column name (from two different tables) is being added twice in the mapping.

That is why the error:

ERROR: NHibernate.MappingException: 'Unable to build the insert statement for class <>.PlannDocument: a failure occured when adding the Id of the class'

ArgumentException: The column 'PLAN_ID' has already been added in this SQL builder Parameter name: columnName

In PlannDocument HBM, column name PLAN_ID is first used while creating id as below:

<id name="PlanId" column="PLAN_ID"  type = "int">

and then, again while creating many-to-one relation as below:

<many-to-one name="Plann" column="PLAN_ID"></many-to-one>

This is causing conflict of column name.

The solution I can think is to change the column name to something defer from the other table. Also, modify the classes and mappings accordingly.

I understand that this cannot be the solution every time and in all the conditions.

回答2:

If you have the same column for identifier and for your desired many-to-one association - it's not really a many-to-one association. Sharing the same identifier means it's one-to-one association. Just use it instead of your many-to-one mapping in PlannDocument.hbm.xml and it should work:

<one-to-one name="Plann" constrained="true" />

If your PlannDocument.Plann can be null than use constrained="false" instead. But be aware that this will cost you additional query to check if Plann really exists.

来源：https://stackoverflow.com/questions/55171918/many-to-many-with-same-id-key-fields

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nhibernate

orm