Sqlite3 foreign keys ignored

constraintforeign keysqlite

I am working on a small sqlite3 database for a small simple mailserver. I have created a new sqlite3 database and add executed this to pürepare it for data:

BEGIN TRANSACTION;
CREATE TABLE `mailboxes` (
    `username`  TEXT NOT NULL,
    `domain`    TEXT NOT NULL,
    `mailbox`   TEXT NOT NULL,
    FOREIGN KEY(`domain`) REFERENCES domains(domain)
    UNIQUE (username, domain),
    UNIQUE (mailbox)
);
CREATE TABLE `domains` (
    `domain`    TEXT NOT NULL UNIQUE
);
CREATE TABLE `aliases` (
    `aliasname` TEXT NOT NULL,
    `domain`    TEXT NOT NULL,
    `destination`   TEXT NOT NULL,
    FOREIGN KEY(`domain`) REFERENCES domains(domain)
    UNIQUE (aliasname, domain)
);
COMMIT;

Foreign keys are enabled with PRAGMA and no errors are shown. As you can see, mailboxes and aliases are nearly the same. I have a list of available domains. Every mailbox/alias entry must use a valid entry of "domains". In addition to this, a "username – domain" pair should only appear once. BUT: the same mail can appear in mailboxes and aliases.

PROBLEM

I have no entries in my domains table, but executing this works (but it should not, because it is not a valid domain):

INSERT INTO aliases (aliasname, domain, destination)
VALUES ('test', 'myacc.de', 'other@worldwide.com');

Where is my fault?

Best Answer

I was partially able to reproduce your bug when having PRAGMA foreign_keys = ON;, but setting the domain column in the domains table as PRIMARY KEY removed any problem in my case. (Still keep the pragma on).

Related Solutions

Pitfalls of creating a foreign key constraint on a system table

I did not find an elegant way to solve this question but adding a check constraint on the "Owner" column of the metadata tables accomplished the objective of ensuring that only schema owners would be listed. If a new schema owner is added then all the check constraints would have to be changed but that is not too onerous.

I tip my hat to Phil for confirming that backing away slowly from system tables is the best approach and wish he had posted this as an answer.

PostgreSQL – insert/update violates foreign key constraints

There are a few problems with your tables. I'll try to address the foreign keys first, since you question asked about them :)

But before that, we should realize that the two sets of tables (the first three you created and the second set, which you created after dropping the first set) are the same. Of course, the definition of Table3 in your second attempt has syntax and logical errors, but the basic idea is:

CREATE TABLE table3 (   
  "ID" bigint NOT NULL DEFAULT '0',   
  "DataID" bigint DEFAULT NULL,   
  "Address" numeric(20) DEFAULT NULL,   
  "Data" bigint DEFAULT NULL,
   PRIMARY KEY ("ID"),   
   FOREIGN KEY ("DataID") REFERENCES Table1("DataID") on delete cascade on update cascade,   
   FOREIGN KEY ("Address") REFERENCES Table2("Address") on delete cascade on update cascade
);

This definition tell PostgreSQL roughly the following: "Create a table with four columns, one will be the primary key (PK), the others can be NULL. If a new row is inserted, check DataID and Address: if they contain a non-NULL value (say 27856), then check Table1 for DataID˙and Table2 for Address. If there is no such value in those tables, then return an error." This last point which you've seen first:

ERROR: insert or update on table "Table3" violates foreign key constraint 
    "Table3_DataID_fkey" DETAIL: Key (DataID)=(27856) is not present in table "Table1".

So simple: if there is no row in Table1 where DataID = 27856, then you can't insert that row into Table3.

If you need that row, you should first insert a row into Table1 with DataID = 27856, and only then try to insert into Table3. If this seems to you not what you want, please describe in a few sentences what you want to achieve, and we can help with a good design.

And now about the other problems.

You define your PKs as

CREATE all_your_tables (
    first_column NOT NULL DEFAULT '0',   
    [...]
    PRIMARY KEY ("ID"),

A primary key means that all the items in it are different from each other, that is, the values are UNIQUE. If you give a static DEFAULT (like '0') to a UNIQUE column, you will experience bad surprises all the time. This is what you got in your third error message.

Furthermore, '0' means a text string, but not a number (bigint or numeric in your case). Use simply 0 instead (or don't use it at all, as I written above).

And a last point (I may be wrong here): in Table2, your Address field is set to numeric(20). At the same time, it is the PK of the table. The column name and the data type suggests that this address can change in the future. If this is true, than it is a very bad choice for a PK. Think about the following scenario: you have an address '1234567890454', which has a child in Table3 like

ID        DataID           Address             Data
123       3216547          1234567890454       654897564134569

Now that address happens to change to something other. How do you make your child row in Table3 follow its parent to the new address? (There are solutions for this, but can cause much confusion.) If this is your case, add an ID column to your table, which will not contain any information from the real world, it will simply serve as an identification value (that is, ID) for an address.

PROBLEM

Best Answer

Related Solutions

Pitfalls of creating a foreign key constraint on a system table

PostgreSQL – insert/update violates foreign key constraints

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