Table Validation when using Foreign Keys

[baalmael]

Currently, when a validating a Schema against a Table an UnsupportedOperationException is thrown if the Schema defines foreign keys to another resource.

java.lang.UnsupportedOperationException: Foreign key references across package resources are not supported

	at io.frictionlessdata.tableschema.fk.ForeignKey.validate(ForeignKey.java:148)
	at io.frictionlessdata.tableschema.schema.Schema.validate(Schema.java:657)
	at io.frictionlessdata.tableschema.Table.validate(Table.java:634)

This means validating headers, primary keys and foreign keys (in resource) is not supported for this usecase (without an exception) without implementing workarounds such as removing all foreign keys before calling table.validate().

I would suggest either:

• Adding real Foreign key validation (not really possible on Table level). See: Support foreign key checks and dereferencing datapackage-java#4
• Split the validation (for example: validateHeaders(), validatePrimaryKeys(), validateForeignKeys(boolean ignoreCrossResource). This would also help with clarity in terms of what is validated