Add Foreign Key Support

[kingmesal]

Adding on to #53 ...

For foreign keys there are a number of options a foreign key may have, but from a definition standpoint adding the foreign key to the column definition make the most sense as each column may only reference a single foreign column.

What I propose is the following:

{
  username: {
    type: DataTypes.STRING,
    unique: "some-arbitrary-key",
  },
  session: {
    type: DataTypes.STRING,
    foreignKey: {
      table: "session-table", // example like Model.tableName
      column: "session-table-field-name", // example like Model.columnName
      onDelete?: {
          cascade?: boolean,
          restrict?: boolean,
          setNull?: boolean,
          setDefault?: boolean,
      },
      onUpdate?: {
          cascade?: boolean,
          restrict?: boolean,
          setNull?: boolean,
          setDefault?: boolean,
      },
    },
  },
}

I think this approach is fairly straight-forward and easy to follow.

Thoughts?

[Skye-31]

Duplicate of #23?

[kingmesal]

Why would foreign key definitions be a duplicate of join syntax ?

Foreign keys are not required to provide join support.

[shynyng]

It seems great. 👍

[chrisspiegl]

Are you planning to add support for the foreign keys and join syntax to build relationships with this ORM?

Would be awesome to fetch things more easily this way.

[Skye-31]

Are you planning to add support for the foreign keys and join syntax to build relationships with this ORM?

Would be awesome to fetch things more easily this way.

@chrisspiegl

Pulls welcome 😃