Question

I’m hoping somebody will be able to help with my SQLite database problem.

I’m receiving a ConstraintException when querying my SQLite database with C#. The full exception message is “Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints.” I originally built this database using access which worked fine, but for various reasons I had to recreate it using SQLite.

To give a bit of background – this is a simple status scheduling program. Each Status has an associated Account and Schedule. I realise Statuses and Schedule is a 1:1 relationship and could be in the same table but to allow the program to develop further I have split them into two tables.

See below for a cut down version of my table script (this is enough to recreate the problem).

PRAGMA foreign_keys = ON;

CREATE TABLE Accounts
(ID INTEGER PRIMARY KEY AUTOINCREMENT,
Name char(100));

CREATE TABLE Statuses
(ID INTEGER PRIMARY KEY AUTOINCREMENT,
AccountId INTEGER REFERENCES Accounts(ID) ON DELETE CASCADE,
Text char(140));

CREATE TABLE Schedule
(ID INTEGER PRIMARY KEY REFERENCES Statuses(ID) ON DELETE CASCADE,
StartDate char(255),
Frequency INT);

I did not have any issues until I created two Statues and associated them to the same Account.

Accounts
ID  Name
1   Fred Blogs

Statuses
ID AccountId Text
1         1          “Some text”
2         1          “Some more text”

Schedule
ID    StartDate     Frequency
1     16/02/2011        1
2     16/02/2011        1

The select statement I’m using which throws the exception is:

SELECT Statuses.Id, Statuses.Text, Accounts.Id, Accounts.Name, Schedule.StartDate, Schedule.Frequency
FROM [Statuses], [Accounts], [Schedule]
WHERE Statuses.AccountId = Accounts.Id AND Statuses.Id = Schedule.Id

If I run the same query, but remove the ‘Accounts.Id’ column the query works fine.

See below for the C# code I’m using but I don’t think this is the problem

public DataTable Query(string commandText)
    {

        SQLiteConnection sqliteCon = new SQLiteConnection(ConnectionString);
        SQLiteCommand sqliteCom = new SQLiteCommand(commandText, sqliteCon);
        DataTable sqliteResult = new DataTable("Query Result");

        try
        {
            sqliteCon.Open();
            sqliteResult.Load(sqliteCom.ExecuteReader());
        }
        catch (Exception)
        {
            throw;
        }
        finally
        {
            sqliteCon.Close();
        }

        return sqliteResult;

    }

Any help will be appreciated. Thanks.

Answer 1

I have found a way round this problem. If I select the AccountId from the Schedule table rather than the Accounts table there is no exception thrown. It seems I was unable to run a SELECT statement that contained two Unique primary key columns.

So instead of

SELECT Statuses.Id, Statuses.Text, Accounts.Id, Accounts.Name, Schedule.StartDate, Schedule.Frequency
FROM [Statuses], [Accounts], [Schedule]
WHERE Statuses.AccountId = Accounts.Id AND Statuses.Id = Schedule.Id

I run

SELECT Statuses.Id, Statuses.Text, Statuses.AccountId, Accounts.Name, Schedule.StartDate, Schedule.Frequency
FROM [Statuses], [Accounts], [Schedule]
WHERE Statuses.AccountId = Accounts.Id AND Statuses.Id = Schedule.Id