What properties does Column columnDefinition make redundant

Question

I often specify my  Column annotations like this    Column columnDefinition  character varying  100  not null  length 100 nullable false    As you can see I specify length and nullable even though the columnDefinition already specifies those  That s because I don t know where when these values are used exactly   So  when specifying columnDefinition  what other properties of  Column are made redundant   If it matters  I use Hibernate and PostgreSQL

User · Answer

columnDefinition will override the sql DDL generated by hibernate for this particular column  it is non portable and depends on what database you are using  You can use it to specify nullable  length  precision  scale    ect

User · Answer

My Answer  All of the following should be overridden  i e  describe them all within columndefinition  if appropriate     length precision scale nullable unique   i e  the column DDL will consist of  name   columndefinition and nothing else   Rationale follows      Annotation containing the word  Column  or  Table  is purely physical - properties only used to control DDL DML against database  Other annotation purely logical - properties used in-memory in java to control JPA processing  That s why sometimes it appears the optionality nullability is set twice - once via  Basic     optional true  and once via  Column     nullable true    Former says attribute association can be null in the JPA object model  in-memory   at flush time  latter says DB column can be null   Usually you d want them set the same - but not always  depending on how the DB tables are setup and reused    In your example  length and nullable properties are overridden and redundant          So  when specifying columnDefinition  what other properties of  Column are made redundant     In JPA Spec  amp  javadoc    columnDefinition definition  The SQL fragment that is used when generating the DDL for the column   columnDefinition default  Generated SQL to create a column of the inferred type  The following examples are provided    Column name  DESC   columnDefinition  CLOB NOT NULL   table  EMP DETAIL    Column name  EMP PIC   columnDefinition  BLOB NOT NULL    And  err     that s it really    -        Does columnDefinition override other properties provided in the same annotation   The javadoc and JPA spec don t explicity address this - spec s not giving great protection  To be 100  sure  test with your chosen implementation  The following can be safely implied from examples provided in the JPA spec   name  amp  table can be used in conjunction with columnDefinition  neither are overridden nullable is overridden made redundant by columnDefinition  The following can be fairly safely implied from  the  logic of the situation   did I just say that    -P      length  precision  scale are overridden made redundant by the columnDefinition - they are integral to the type insertable and updateable are provided separately and never included in columnDefinition  because they control SQL generation in-memory  before it is emmitted to the database   That leaves just the  unique  property   It s similar to nullable -  extends qualifies the type definition  so should be treated integral to type definition   i e  should be overridden      Test My Answer For columns  A   amp   B   respectively      Column name        table        insertable true  updateable false            columndefinition  NUMBER 5 2  NOT NULL UNIQUE      Column name        table        insertable false  updateable true            columndefinition  NVARCHAR2 100  NULL     confirm generated table has correct type nullability uniqueness optionally  do JPA insert  amp  update  former should include column A  latter column B

[java] What properties does @Column columnDefinition make redundant?

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