How to Tell JPA the prefered DataType

问题

If I use JPA (EclipseLink) to create tables a String type results in a varchar2(255). How could I tell JPA (via Annotation) to create a varchar2(20) attribute.

If I have a List JPA creates a BLOB(4000) but I would like a varchar2 (my serialized object's string is short)

How is this possible? Do I have to do it by hand?

回答1:

You need to use the columnDefinition property of the @Column annotation. i.e.

@Column(columnDefinition="varchar2(20)")

回答2:

If I use JPA (EclipseLink) to create tables a String type results in a varchar2(255). How could I tell JPA (via Annotation) to create a varchar2(20) attribute.

Using the columnDefinition can break portability from one database to another. For a string-valued column, prefer using the length element (which defaults to 255):

@Column(length=20)
String someString;

回答3:

You can set the length on your @Column annotation, as such:

@Column(length = 20)

Note that length is only for text columns. For numeric, you can use precision and scale.

回答4:

@Column(name = "doc_number", columnDefinition = "varchar2(20)")

Please, try that.

来源：https://stackoverflow.com/questions/4088400/how-to-tell-jpa-the-prefered-datatype