Add validate method to BaseMultiTableSynthesizer

[amontanez24]

Problem Description

As a user, it would be useful to see if the data I provide matches my metadata at the multi-table level.

Acceptance criteria

• Add a method called validate to the BaseMultiTableSynthesizer class
  • This method should have the following parameters:
    • data: a dictionary mapping table name -> the pandas DataFrame for that table
  • The method should call the SingleTableSynthesizer.validate to accumulate those errors
  • Additionally, it should perform the following check: Columns marked as foreign keys should be referencing a primary key that exists in the parent table – ie no unknown parent references.
    • If this fails raise the following error:
      Error: Foreign key column 'purchaser_id' contains unknown references: ('Unknown', 'USER_999', 'ZZZ', +more). All the values in must reference a primary key.

Expected behavior

>>> synthesizer = HMASynthesizer(metadata)
>>> synthesizer.validate(data)

InvalidDataError: The provided data does not match the metadata

Error: Foreign key column 'purchaser_id' contains unknown references: ('Unknown', 'USER_999', 'ZZZ', +more). All the values in must reference a primary key.