insert or update on table violates foreign key constraint

Question

I have two tables: entitytype and project. Here are the create table statements:

Create table project ( 
pname varchar(20) not null, 
primary key(pname)
);

create table entitytype( 
entityname varchar(20) not null, 
toppos char(100), 
leftpos char(100), 
pname varchar(20) not null, 
primary key(entityname), 
foreign key(pname) references project(pname) on delete cascade on update cascade
);

When I try to insert any values into the entitytype table, I get the following error:

ERROR: insert or update on table "entitytype" violates foreign key constraint "entitytype_pname_fkey"
  Detail: Key (pname)=(494) is not present in table "project".

Can anyone shed some light on what I am doing wrong?

Answer 1

The error message means you are attempting to add an entityType that does not have a corresponding Project entry. (I don't know your domain or what you are trying to achieve, but that schema design looks wrong to me...)

Answer 2

Do you not have a record in table project with a pname of (in your example) 494?

The key relationship says no pname is allowed in the entity table unless it matches a pname in the project table.