Oracle SQL, trigger inserting row into table X as FK for currently inserted row in table Y - sql

Question

So in Oracle 11g I have the following:
CREATE TABLE OBJECT(
ID NUMBER(8) NOT NULL,
CATEGORY_ENUM_ID NUMBER(8) NOT NULL
);
CREATE SEQUENCE OBJECT_SEQ
START WITH 1
INCREMENT BY 1
NOCACHE
NOCYCLE;
/
CREATE TABLE TREE(
ID NUMBER(8) NOT NULL,
OBJECT_ID NUMBER(8) NOT NULL,
NAME NVARCHAR2(128)
);
CREATE TABLE CATEGORY_ENUM(
ID NUMBER(8) NOT NULL,
NAME NVARCHAR2(64)
);
-- PK's
ALTER TABLE TREE
ADD CONSTRAINT TREE_PK PRIMARY KEY (ID);
ALTER TABLE OBJECT
ADD CONSTRAINT OBJECT_PK PRIMARY KEY (ID);
ALTER TABLE CATEGORY_ENUM
ADD CONSTRAINT CATEGORY_ENUM_PK PRIMARY KEY (ID)
--- FK's
ALTER TABLE TREE
ADD CONSTRAINT TREE_OBJECT_FK FOREIGN KEY (OBJECT_ID)
REFERENCES OBJECT (ID);
ALTER TABLE OBJECT
ADD CONSTRAINT OBJECT_CATEGORY_FK FOREIGN KEY (CATEGORY_ENUM_ID)
REFERENCES CATEGORY_ENUM (ID);
-- Closed dictionary sample data
INSERT INTO CATEGORY_ENUM (ID, NAME) VALUES (1, 'TREE');
INSERT INTO CATEGORY_ENUM (ID, NAME) VALUES (2, 'HERB');
INSERT INTO CATEGORY_ENUM (ID, NAME) VALUES (3, 'SHROOM');
-- Triggers
CREATE OR REPLACE TRIGGER TREE_before_insert
BEFORE INSERT
ON TREE
REFERENCING NEW AS NEW OLD AS OLD
FOR EACH ROW
DECLARE
CATEGORY_ID NUMBER;
BEGIN
SELECT ID INTO CATEGORY_ID FROM CATEGORY_ENUM WHERE NAME = 'TREE' AND ROWNUM <= 1;
if :NEW.OBJECT_ID is null then
:NEW.OBJECT_ID := OBJECT_SEQ.nextval;
INSERT INTO OBJECT (ID, CATEGORY_ENUM_ID) VALUES (:NEW.OBJECT_ID, CATEGORY_ID);
end if;
END;
/
If next I run:
INSERT INTO TREE (ID, NAME) VALUES (1, 'Tree1');
INSERT INTO TREE (ID, NAME) VALUES (2, 'Tree2');
I get an error:
...
TRIGGER TREE_BEFORE_INSERT compiled
Error starting at line 91 in command:
INSERT INTO TREE (ID, NAME) VALUES (1, 'Tree1')
Error report:
SQL Error: ORA-02291: integrity constraint (HR.TREE_OBJECT_FK) violated - parent key not found
02291. 00000 - "integrity constraint (%s.%s) violated - parent key not found"
*Cause: A foreign key value has no matching primary key value.
*Action: Delete the foreign key or add a matching primary key.
1 rows inserted.
But if before the above, I insert anything into FEATURES table (like below), it works fine.
INSERT INTO OBJECT (ID, CATEGORY_ENUM_ID) VALUES (0, 1);
INSERT INTO TREE (ID, NAME) VALUES (1, 'Tree1');
INSERT INTO TREE (ID, NAME) VALUES (2, 'Tree2');
So the problem occurs only for the very first insert, the others work fine, IDs assigned from OBJECT_SEQ.nextval are proper.
What am I doing wrong ?
Jah bless ya for help.
EDIT I have removed some unnecessary code, so now it's more clear and shorter.

Answer 1

The problem here is that you have a primary key constraint placed on the "TREE" table and a foreign key constraint placed on the "OBJECT" table. So any new record that you try inserting into the table with foreign key constraint, make sure it is already available in the table that has the primary key mapping.
Example shown below:
**Tables:**
create table tab1
(id number,
name varchar2(100)
)
create table tab2
(id number,
name varchar2(100)
)
**constraints added:**
alter table tab1 add constraint pk_tab1_id primary key (id)
alter table tab2 add constraint fk_tab2_id foreign key(id) references tab1(id)
**Insert statement on the second table:**
insert into tab2(values(1,'abc')
**Error:**
SQL Error: ORA-02291: integrity constraint (PRAVE.fk_tab2_id) violated - parent key not found
02291. 00000 - "integrity constraint (%s.%s) violated - parent key not found"
*Cause: A foreign key value has no matching primary key value.
*Action: Delete the foreign key or add a matching primary key.
**Solution:**
**Insert into the table with PK first as below:**
insert into tab1 values(1,'abc')
1 rows inserted.
insert into tab2 values(1,'abc')
1 rows inserted.