ManyToMany properties

This may be a stupid question or may be asked, But i didnt find which helped me. Can anyone of you guys tell me what these properties described in ManyToMany relation do. And if there are any which i missed and should be used i开发者_运维问答n ManyToMany mapping please help me with that too.

@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "customer_service",
    joinColumns = {@JoinColumn(name = "customer_id")},
    inverseJoinColumns = @JoinColumn(name = "service_id"))

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This is description of a many-to-many relationship between (I am guessing) Customer and Service tables. Technically all attributes are optional so:

@ManyToMany
private Set<Customer> services;

in Service would be fine (similar annotation on Customer side if the relationship is bidirectional).

Now assuming you have a some basic relational databases design knowledge:

• @JoinTable describes a join table, the one used to store relationships between customer and service. Each row contains one reference to customer and one to service. This table will be named customer_service

• joinColumns - definition of column(s) referencing the second side of the relationship - customer_id

• inverseJoinColumns - definition of column(s) referencing back to the starting side - service_id in this example.

Join- and inverse join columns are symmetric - if you define the many-to-many relationship on the other side you switch them. Otherwise everything will work from Java perspective but Hibernate will create a foreign key from customer_id to Service table and vice-versa and will insert values accordingly.