Foreign key constraints with nullable references

[TravisCardwell]

The current API does not provide a way to annotate a table with a foreign key constraint when the column is nullable. This type of constraint is very common, as it used for optional one-to-one relations (often marked as ? or 0|1 in database software).

I implemented new functions nullableForeignKeyOnPk and nullableForeignKeyOn to support this, and I will submit a pull request.

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tc-develop Documentation