postgres jdbc insert array of custom type

Question

I want to insert array of custom type into postgres with jdbc .

my sql schema:

CREATE TYPE element_pk_t AS (
    workspace_id   BIGINT,
    element_id     BIGINT,
    history_id     BIGINT
);

my java class:

public class ElementPK {
    public Long workspaceId;

    public Long elementId;

    public Long historyId;
}

How should I do this in java with jdbc ?

I've found tutorial regarding custom type https://docs.oracle.com/javase/tutorial/jdbc/basics/sqlcustommapping.html , but array of custom type is still unclear to me.

One trivial approach is using pure string style SQL statement, but I still prefer using PreparedStatement with setObject or setArray

Answer 1

If I understood you correctly, then, from the Java code, you need to generate query that looks, for example, like this:

INSERT INTO parent_table(elements) 
VALUES (
ARRAY[
     row(1, 2, 3)::element_pk, 
     row(4, 5, 6)::element_pk, 
     row(7, 8, 9)::element_pk
]);

Assuming that you have a table like the following:

CREATE TABLE parent_table(
    id SERIAL PRIMARY KEY,
    created_at TIMESTAMPTZ DEFAULT NOW(),
    elements element_pk[]
)

And the Type like you described. If I were you, I wont implement it via an array. I would have use JSONB instead - in this way you wont lose an ability to use indexing. Of course, there is java.sql.Array out there, and you can still do it via the following:

Array array = connection.createArrayOf("public.element_pk", new ElementPK[]{
                new ElementPK(1, 2, 3),
                new ElementPK(9, 4, 6)
        });

And then set the array, to PgPreparedStatement , but the thing is that internally PgPreparedStatement will enclose your elements within curly braces, which is ok, but each element will be represented by its toString method call result. I mean, assume your ElementPK toString looks like this:

    @Override
    public String toString() {
        return "This is how it is implemented, really?";
    }

then you will get the SQL like:

INSERT INTO parent_table (elements) VALUES ('{"This is how it is implemented, really?","This is how it is implemented, really?"}')

Again, it is maybe possible to adopt it, but from my perspective - at least having your logic within toString method is not that great, is it? Spare yourself and do the following:

CREATE TABLE via_jsonb(
    elements JSONB
);

and then simply:

INSERT INTO via_jsonb VALUES(
'{
    "workspace_id" : 1,
    "element_id" : 2,
    "history_id" : 3
 }'
);

and in the Java code I would have simply create json from your object and set it as a string. Really, there are a lot of functions and cool features on JSONB out of the box.

Hope it helped, have a nice day!)

Answer 2

Follow up to the last part of @misha2045 answer.

If you still refuese to use JSONB for whatever reason you need to add parenthesis at the end and start of your toString method.

@Override
public String toString() {
    return "("+this.field1+ ", " + this.field2+")";
}

Then set the array in the prepared statement

ps.setArray(1, con.createArrayOf("yourType", yourClassArray));