Default values and not null constraints

Question

spring-boot-starter-parent 2.4.1

spring-boot-starter-data-jpa

postgres 12.5

A short excerpt from an entity:

import lombok.Getter;
import lombok.Setter;

@Getter
@Setter    

@Entity
public class Branch extends BaseEntity{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;    

    @Column(columnDefinition = "varchar(255) default ''", nullable = false)
    private String name;

    @Column(columnDefinition = "varchar(255) default ''")
    private String segmentFour;
}

The entity generates a table like this:

This is it:

ads=# \d clients__branch

                                          Table "public.clients__branch"
            Column         |          Type          | Collation | Nullable |             Default              
    -----------------------+------------------------+-----------+----------+----------------------------------
     id                    | integer                |           | not null | generated by default as identity
     name                  | character varying(255) |           | not null | ''::character varying
     segment_four          | character varying(255) |           |          | ''::character varying
 

We can see that:

1. "name" is not null and has a default value ''.
2. "segment_one" has a default value, but there is no not null constraint.

Let's try to use this.

Let's fill the data and save it:

Branch branch0 = new Branch();
branch0.setName("Train");
branch0.setSegmentFour("");


Branch branch1 = new Branch();
branch1.setName("Car");
branch1.setSegmentFour(null);

Branch branch2 = new Branch();
branch2.setName("Ship");

Result:

ads=# select id, name, case when segment_four is null then 'null' when segment_four = '' then 'space' end as segment from clients__branch;
 id |  name   | segment 
----+---------+---------
  1 | Vosst   | space
  2 | Ryba    | null
  3 | Admiral | null

Problems

1. I'd like to prevent anybody to from setting Null as in case with branch1.

2. If I organize it like this:

   @Column(columnDefinition = "varchar(255) default ''", nullable = false) private String segmentFour;

   then I get:

   ERROR: null value in column "segment_four" violates not-null constraint
   

3. I'd like to have a default value (the code for branch2 should generate '' in the segment_four).

Could you help me?

Answer 1

I don't think there is a direct way to handle this using @Column annotation, but you can own logic in the setter method to make it to empty if value is null

public void setSegmentFour(String segmentFour) {
 this.segmentFour = segmentFour == null ? "" : segmentFour;
 }

Answer 2

I would suggest you to use @ColumnDefault with @DynamicInsert in the following way:

@Entity
@DynamicInsert
public class Branch extends BaseEntity{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;    

    @Column
    @ColumnDefault("''")
    private String name;

    @Column
    @ColumnDefault("''")
    private String segmentFour;
    
    // ...
}

and then just omit to set value for the field if you want to use the default value. The entity above is annotated with the @DynamicInsert annotation so that the INSERT statement does not include any entity attribute that does not contain a value.

See additional explanation in the documentation.