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Couchbase 5.0 Dev Build: Feature Enhancements to N1QL

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Couchbase 5.0 Dev Build: Feature Enhancements to N1QL

Couchbase 5.0's latest dev build hopes to enhance N1QL features such as simplified array indexing and relaxed variable matching.

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With the recent March 2017 Developer build of Couchbase there were many bug fixes, but also feature enhancements to core technologies like N1QL. For example, now indexes can be created on various meta information such as the document CAS and expiration values. Another example includes a simplified syntax when creating array indexes.

We’re going to take a look at some of these enhancements and how you might use them in your own application.

Simplified Array Indexing in Couchbase 5.0

With Couchbase Server 4.5 came the array indexing. Take the following sample document for example:

{
  "type": "person",
  "firstname": "Nic",
  "lastname": "Raboy",
  "social-media": [
    {
      "type": "twitter",
      "url": "https://www.twitter.com/nraboy"
    },
    {
      "type": "website",
      "url": "https://www.thepolyglotdeveloper.com"
    }
  ]
}


New Array Index Syntax

Before Couchbase 5.0, to index the array elements found in social-media you had to write an index that looked something like the following:

CREATE INDEX ism 
ON `default` ( DISTINCT ARRAY media FOR media IN `social-media` END )
WHERE type = 'person';


In the above example, the FOR operator was necessary for array indexing. In Couchbase Server 5.0 there is a much more simplified syntax. The same index can be created via the following:

CREATE INDEX ism 
ON `default` ( DISTINCT `social-media` )
WHERE type = "person";


To make sure your index works, you can execute the following N1QL query:

EXPLAIN SELECT *
FROM default
WHERE type = 'person' AND ANY media IN `social-media` SATISFIES media.type = 'website' END;


When looking through the results of the EXPLAIN you should see that it is using the ismindex that was previously created.

Now just because the simplified syntax exists doesn’t mean you can’t use the previous syntax when array indexing. The following would be a perfect example of why the previous syntax would still be valid:

CREATE INDEX ism_website
ON `default` ( DISTINCT ARRAY media FOR media IN `social-media` WHEN media.type = 'website' END )
WHERE type = 'person';


Notice that a WHEN operator was used when creating the ism_website index above.

More information on array indexing can be found here, along with other useful documentation on creating indexes in Couchbase.

Relaxed Variable Match Requirement for Array Indexes

In 4.x releases, the array indexing required usage of exactly same variable names in the SELECT query that were used in the CREATE INDEX statement. Find more details here.

For example, referring to the previous queries seen above, note that the variable media, which is used to iterate through the array social-media , is very important. Array indexing in 4.x mandates the exact variable name media to be used in the previous SELECT query.

The Couchbase 5.0 release relaxes this requirement, and the following query would work perfectly fine:

EXPLAIN SELECT *
FROM default
USE INDEX (ism)
WHERE type = 'person' AND ANY m IN `social-media` SATISFIES m.type = 'website' END;


Note that, the index ism uses the variable name media, but the query above uses m. Still, the above query can use the index ism successfully.

A Relaxed Whole Array Index Key Requirement for Array Indexes

Also recall, in 4.x releases, the covered array indexing requires the whole array attribute as a mandatory index-key in the array index definition. For example, take the following query again:

EXPLAIN SELECT *
FROM default
WHERE type = 'person' AND ANY media IN `social-media` SATISFIES media.type = 'website' END;


The covered array index corresponding to the above query would be:

CREATE INDEX ism_covered 
ON `default` ( DISTINCT ARRAY media FOR media IN `social-media` END,  `social-media`)
WHERE type = 'person';


Note that, the second index key social-media is mandatory, for example to cover following query:

EXPLAIN SELECT media
FROM default
WHERE type = 'person' AND ANY media IN `social-media` SATISFIES media IS NOT NULL END;


In Couchbase 5.0, this same query will be covered by index ism at the very start of this article.

It is important to note that, this feature brings lot of power to Array Indexes. Because, now each entry in the array index consumes less storage space and memory. It enables following benefits:

  • Usage of covered array indexes for larger arrays
  • Brings more efficiency and performance to queries using covered array indexes

Indexing Document Meta Information

Let’s take a turn here and discuss the new meta information that can be indexed. Previously indexes could be created on the meta().id property, but now both the meta().cas and meta().expiration properties are supported.

So how do we create an index that uses the meta properties as keys? It isn’t any different from what you already know. Take the following covering indexes for example:

CREATE INDEX idx_cas
ON `default` ( META().cas, META().expiration )

CREATE INDEX idx_exp
ON `default` ( META().expiration )


Now, if I wanted to use the idx_cas and idx_exp indexes in a N1QL query, I could do something like the following:

SELECT META().id, META().cas
FROM default
WHERE META().cas > 1489531586248179712;

SELECT META().id, META().expiration
FROM default
WHERE META().expiration > NOW_MILLIS();


So why would being able to index these properties be a benefit? Well, what if you wanted to do a query for all documents that had expired today or all documents that were modified today?

For more information on the CAS and expiration properties, visit here. For more information on indexing or using N1QL with Couchbase, check out the Couchbase Developer Portal.

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Topics:
n1ql ,couchbase 5.0 ,database ,tutorial ,query performance

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