Run CouchDB Mango - (CouchDB Tutorial)

CouchDB is a popular NoSQL database that uses JSON to store data. One of the powerful features of CouchDB is Mango, which allows users to perform advanced queries on their data using a simple syntax. In this tutorial, we'll discuss how to run Mango queries in CouchDB.

Syntax

{
   "selector": { /* the query selector */  },
   "fields": [ /* the fields to return */  ],
   "sort": [ /* the sort order */ ],
   "skip": /* the number of records to skip */,
   "limit": /* the maximum number of results to return */
}

• selector: The query selector, which contains the conditions that your documents must meet.
• fields: An array of field names to return in the result set.
• sort: An array of sort order conditions.
• skip: The number of records to skip before returning results.
• limit: The maximum number of results to return.

Example

Let's say we have a database of books with the following structure:

{
  "_id": "1",
  "_rev": "1-234567890",
  "title": "The Great Gatsby",
  "author": "F. Scott Fitzgerald",
  "rating": 4.5,
  "published": "1925-04-10"
}

We can use Mango queries to find books by author, rating, and publication date with the following syntax:

{
  "selector": {
    "author": "F. Scott Fitzgerald",
    "rating": {
      "$gt": 4
    },
    "published": {
      "$gt": "1920-01-01"
    }
  },
  "fields": [
    "title",
    "author",
    "published"
  ],
  "sort": [
    {
      "published": "desc"
    }
  ],
  "skip": 0,
  "limit": 10
}

This query will return books by F. Scott Fitzgerald with a rating greater than 4 and published after 1920-01-01, sorted by publication date in descending order, and limited to 10 results. The result set will include only the title, author, and publication date fields.

Output

The output of this query will be a JSON array of book documents that match the specified conditions, sorted by publication date in descending order, and limited to 10 results. The result set will include only the title, author, and publication date fields.

[
  {
    "title": "The Great Gatsby",
    "author": "F. Scott Fitzgerald",
    "published": "1925-04-10"
  },
  {
    "title": "Tender Is the Night",
    "author": "F. Scott Fitzgerald",
    "published": "1934-04-01"
  },
  {
    "title": "This Side of Paradise",
    "author": "F. Scott Fitzgerald",
    "published": "1920-03-26"
  }
]

Explanation

The Mango query syntax is a simple JSON object with several optional parameters.

The selector parameter is a JSON object that contains the conditions that documents must meet. The fields parameter is an array of the fields to return in the response. The sort parameter is an array of sort order conditions, and the skip and limit parameters dictate how many records to skip and how many to return, respectively.

In this example, we used a query to find books by F. Scott Fitzgerald with a rating greater than 4 and published after 1920-01-01. We returned only the title, author, and publication date fields and sorted the result set by publication date in descending order.

Use

Mango queries in CouchDB are useful for querying data using a simple, flexible syntax. You can use Mango queries to find documents by multiple conditions, sort result sets, and limit results to a certain number.

Important Points

• Mango queries require an index to be created before they can be used.
• You can create indexes using the CouchDB web interface, the couchindex command-line tool, or other tools.
• Mango queries are flexible and can be used to search for data in a variety of ways.

Summary

In this tutorial, we discussed how to run Mango queries in CouchDB. We covered the syntax, example, output, explanation, use, and important points of Mango queries. With this knowledge, you can use Mango queries to search your CouchDB database for data based on multiple conditions and specifications.