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 Post subject: Specifying multiple one-to-one relationships between tables
PostPosted: Sat Aug 19, 2017 8:04 am 
Newbie

Joined: Sat Aug 19, 2017 7:57 am
Posts: 2
There are two tables: Airplane and Engine

Engine: [Engine_ID, Engine_Name, Engine_Position, Airplane_Owner_ID].
Airplane: [Airplane_ID, Airplane_Name,...]
Engine_Position = {Right, Left}

Each plane has two engine (Left_Engine and Right_Engine). And a unique constraint on Engine (Airplane_Owner_ID, Engine_Position).
Therefore there are two one-to-one relationships defined between the Airplane and Engine tables.

How can these relationships be specified in Hibernate and related class in JPA?


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 Post subject: Re: Specifying multiple one-to-one relationships between tables
PostPosted: Sat Aug 19, 2017 11:05 am 
Hibernate Team
Hibernate Team

Joined: Thu Sep 11, 2014 2:50 am
Posts: 1630
Location: Romania
The best way to do it is to change the schema as follows:

Engine: [Engine_ID, Engine_Name].
Airplane: [Airplane_ID, Airplane_Name, Left_Engine_ID, Right_Engine_ID]

This is a much better approach since you said that an engine can only have 2 engines. Using your previous schema, an airplane could end-up with 100 left engines and 300 right ones.


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 Post subject: Re: Specifying multiple one-to-one relationships between tables
PostPosted: Sat Aug 19, 2017 3:36 pm 
Newbie

Joined: Sat Aug 19, 2017 7:57 am
Posts: 2
vlad wrote:
The best way to do it is to change the schema as follows:

Engine: [Engine_ID, Engine_Name].
Airplane: [Airplane_ID, Airplane_Name, Left_Engine_ID, Right_Engine_ID]

This is a much better approach since you said that an engine can only have 2 engines. Using your previous schema, an airplane could end-up with 100 left engines and 300 right ones.

Would you please tell me the jpa?


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 Post subject: Re: Specifying multiple one-to-one relationships between tables
PostPosted: Sun Aug 20, 2017 1:42 am 
Hibernate Team
Hibernate Team

Joined: Thu Sep 11, 2014 2:50 am
Posts: 1630
Location: Romania
Sure. Here's the best way to map a @OneToOne relationship with JPA and Hibernate.


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