具有SQLite和外键的C＃

Question

I want to implement a patients data base for our software, and have an issue with the foreign key statement. I am using the latest SQLite DLLs, with C#.

When I try to run below code:

dbConnection = "Data Source=SQLiteMyDatabase.db;foreign keys=true;";
if (connections == 0)
{
  cnn = new SQLiteConnection(dbConnection);
  cnn.Open();
  this.ExecuteNonQuery("CREATE TABLE IF NOT EXISTS patients ( id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, name VARCHAR(100) NOT NULL;");
  this.ExecuteNonQuery("CREATE TABLE IF NOT EXISTS images ( FOREIGN KEY (patientID) REFERENCES patients(id), nameRed VARCHAR(20) NOT NULL PRIMARY KEY;");
}

I get the error:

SQLite error near "FOREIGN": syntax error

Why does this happen?

Answer 1

In order to create a foreign key, you must first create the column:

CREATE TABLE IF NOT EXISTS images (
    nameRed VARCHAR(20) NOT NULL PRIMARY KEY, 
    patientID INT, 
    FOREIGN KEY (patientID) REFERENCES patients(id) 
 );

Please note:

1. I moved the primary key column ( nameRed ) first in the list of columns created, but that's just convention. It could go second.
2. You use the data type VARCHAR and SQlite will accept that, but be aware that it gets mapped to type TEXT, the maximum length will be ignored, and you will be able to store other data types in the column. SQLite is a bit funny when it comes to data types (it has a very well thought-out system but it's quite different from most other SQL databases).
3. To make things more confusing, you are allowed to declare the PRIMARY KEY as a property of the column (although you can also do it after the list of columns as with the FOREIGN KEY).