Key/Value pairs in a database table

Question

I need to design a Key/value table in my database and I\'m looking for guidance on the best way to do this. Basically, I need to be able to associate values to a dynamic se

Answer 1

Key value pair is generally not a good use of relational databases. the benefits of relational databases are the constraints, validation and structure that goes with it. By using a generic key-value structure in your table you are losing the validation and constraints that make relational databases good. If you want the flexible design of key value pairs, you would be best served by a NoSQL database like MongoDB or its ilk.

Key value pair (e.g. NoSQL databases) works best when the underlying data is unstructured, unpredictable, or changing often. If you don't have structured data, a relational database is going to be more trouble than its worth because you will need to make lots of schema changes and/or jump through hoops to conform your data to the ever-changing structure.

KVP / JSON / NoSql is great because changes to the data structure do not require completely refactoring the data model. Adding a field to your data object is simply a matter of adding it to the data. The other side of the coin is there are fewer constraints and validation checks in a KVP / Nosql database than a relational database so your data might get messy.

There are performance and space saving benefits for relational data models. Normalized relational data can make understanding and validating the data easier because there are table key relationships and constraints to help you out. This will make your application easier to maintain and support in the long term. Another approach is to use a data abstraction layer in your code, like Django or SQL Alchemy for Python, Entity Framework for .NET. That way as your code changes your database will change with it automatically.

One of the worst patterns i've seen is trying to have it both ways. Trying to put a key-value pair into a relational database is often a recipe for disaster. I would recommend using the technology that suits your data foremost.