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Cosmos DB Custom App Logic in Functions

Hasan Savran shows off how we can use user-defined functions to add custom application logic to operations in Cosmos DB:

There are couple of things you need to know about them. First, User-defined functions are only for reading data. User-defined functions will always require more Request Units than regular SQL queries. You should always try to solve your application logic problem with regular queries first. Get familiar with system functions, be sure that you are not trying to write a user-defined function when there is already a system function solving the same problem. System functions will always use less Request Units than your custom user-defines function. Just like SQL Server, User-defined functions will cause a table-scan in Cosmos DB. That is why they cost more than regular queries. If you want to use the User-defined function in a where clause. Try to filter by other properties too. Other properties might hit to indexes and that will help you with request units.

Click through to see an example of them in action.