Hibernate -- Mapping a view with a single value to a read-only field

(Hibernate 3.6, Mysql 5)

I have a mapped class called 'Program' (that is working correctly).

I also have a view that is updated 开发者_C百科daily with aggregate statistics.

The view schema is like so:

view ProgramSummary {
     long program_id
     long value
}

program_id is unique, but there is no row-id. What I want is to just pull the value out, but I can't seem to figure out the right semantics.

I have tried mapping a separate entitiy with a OneToOne (and ManyToOne) relationship, but it gets confused between the ids. Without marking program_id as an entity, hibernate can't handle the actual mapping.

Is there a simple way to do this? It is a read-only field that is accessed by an external process and I don't have any leeway for changing the schema.

You can use a formula in your Program hbm file to map this.

<property name="SummaryValue" type="long" formula="(SELECT value FROM ProgramSummary WHERE ProgramSummary.program_id = id)" />

Assuming your field is named SummaryValue this line will update that field in the Program object. Any field mapped with a formula is not updateable.

If you map a second entity, you might want to set the columns to updatable=false and insertable=false, making them readonly.

However, why don't you just select the value from ProgramSummary, probably with plain SQL?