Object Query Language (OQL) In NCache

Your application typically uses cache as a Hashtable where everything is stored based on a key and you must have this key to fetch an item. This is like having a relational database where you can use only the primary key to find data. This works fine in many situations but a real life complex application often needs to find data based on attributes other than just the primary key. And since you are keeping a lot of your data in the cache, it would be very useful if you could search the cache in this manner as well. A basic example of this would be an e-commerce website that needs to fetch all products based on criteria such as category, price, and weight etc. You cannot specify category based keys for all products and hence cannot store the list of those keys for retrieval.

For searching purposes, NCache provides you with its own powerful cache searching mechanism where you can fetch the cache keys/data using SQL like query syntax.

NCache allows you to search and delete result sets according to your query criteria. However, it does not support insertion/updating on the basis of any query criteria.

To retrieve the data according to your specified non-primary-key criteria, NCache provides you with OQL (Object Query Language) which is the subset of SQL. OQL lets you search the cache against a criteria on which the data is required.

For the scenario highlighted above, you just have to select all the products related to the required category and it will return all related keys or items.

Sample query: "SELECT Product WHERE this.Category = ?"

You can use a rich set of operators provided by NCache according to your required query criteria to fetch desired result sets from your cache.

Note

Object Query Language is not case sensitive.

The following operator categories are supported in NCache queries:

Category	Operator
Basic Query Operators	= , == , != , <> , < , > , <=, >=, IN, LIKE , NOT LIKE
Logical Operators	AND , OR , NOT
Aggregate Functions	SUM, COUNT, AVG, MIN, MAX
Miscellaneous	DateTime.Now , DateTime ("any date time compatible string")