CouchDB: The Definitive Guide

Chapter 21. View Cookbook for SQL Jockeys

This is a collection of some common SQL queries and how to get the same result in CouchDB. The key to remember here is that CouchDB does not work like an SQL database at all and that best practices from the SQL world do not translate well or at all to CouchDB. This chapter’s “cookbook” assumes that you are familiar with the CouchDB basics such as creating and updating databases and documents.

Using Views

How you would do this in SQL:

CREATE TABLE

or:

ALTER TABLE

Using views is a two-step process. First you define a view; then you query it. This is analogous to defining a table structure (with indexes) using CREATE TABLE or ALTER TABLE and querying it using an SQL query.

Defining a View

Defining a view is done by creating a special document in a CouchDB database. The only real specialness is the _id of the document, which starts with _design/—for example, _design/application. Other than that, it is just a regular CouchDB document. To make sure CouchDB understands that you are defining a view, you need to prepare the contents of that design document in a special format. Here is an example:

{
  "_id": "_design/application",
  "_rev": "1-C1687D17",
  "views": {
    "viewname": {
      "map": "function(doc) { ... }",
      "reduce": "function(keys, values) { ... }"
    }
  }
}

We are defining a view viewname. The definition of the view consists of two functions: the map function and the reduce function. Specifying a reduce function is optional. We’ll look at the nature of the functions ...