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dkubb / axiom

Simplifies querying of structured data using relational algebra
https://github.com/dkubb/axiom
MIT License
459 stars 22 forks source link

Add key support to relations #16

Closed dkubb closed 11 years ago

dkubb commented 11 years ago

This branch adds key support to relations. It introduces a new object called Relation::Keys, which is basically a set of Relation::Header objects, each of them representing a candidate key. A Relation::Header#keys attribute stores a reference to the keys for the relation.

dkubb commented 11 years ago

This code is looking close to what I wanted when I started on it.

The remaining task is to add an assertion to the constructor to ensure the keys are irreducible. For example, given the following:

Veritas::Relation::Keys.coerce([ header.project([ :id, :name ]), header.project([ :id ]) ])

Two headers were provided, yet the second is a proper subset of the first. This should cause an exception to be raised. Every key must not be a proper subset of another key.

dkubb commented 11 years ago

fwiw, I decided to add the key irreducibility check in another branch. This one was functional, so I wanted to get it merged into master sooner rather than later.