Java Reference
In-Depth Information
Listing 2.9. EntityManager operations in the BidDao
The true magic of the code in this listing lies in the EntityManager interface. One in-
teresting way to think about the EntityManager interface is as an interpreter between
the object-oriented and relational worlds. The manager reads the O/R mapping annotations
like @Table and @Column on the Bid entity and figures out how to save the entity into
the database. The EntityManager is injected into the DefaultBidDao bean through
the @PersistenceContext annotation
In the addBid method, the EntityManager persist method is called to save the
Bid data into the database . After the persist method returns, an SQL statement
much like the following is issued against the database to insert a record corresponding to
the bid:
VALUES (52, 60, 200.50, 100)
It might be instructive to look back at listing 2.7 now to see how the EntityManager
figures out the SQL to generate by looking at the O/R mapping annotations on the Bid
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