Indexing JSON documents

In addition to indexing Redis hashes, RediSearch also indexes JSON. To index JSON, you must use the RedisJSON module.

Prerequisites

What do you need to start indexing JSON documents?

• Redis 6.x or later
• RediSearch 2.2 or later
• RedisJSON 2.0 or later

How to index JSON documents

This section shows how to create an index.

You can now specify ON JSON to inform RediSearch that you want to index JSON documents.

For the SCHEMA, you can provide JSONPath expressions. The result of each JSON Path expression is indexed and associated with a logical name (attribute). This attribute (previously called field) is used in the query.

This is the basic syntax to index a JSON document:

FT.CREATE {index_name} ON JSON SCHEMA {json_path} AS {attribute} {type}

And here's a concrete example:

FT.CREATE userIdx ON JSON SCHEMA $.user.name AS name TEXT $.user.tag AS country TAG

Adding a JSON document to the index

As soon as the index is created, any pre-existing JSON document, or any new JSON document added or modified, is automatically indexed.

You can use any write command from the RedisJSON module (JSON.SET, JSON.ARRAPPEND, etc.).

This example uses the following JSON document:

{
  "user": {
    "name": "John Smith",
    "tag": "foo,bar",
    "hp": "1000",
    "dmg": "150"
  }
}

Use JSON.SET to store the document in the database:

JSON.SET myDoc $ '{"user":{"name":"John Smith","tag":"foo,bar","hp":1000, "dmg":150}}'

Because indexing is synchronous, the document will be visible on the index as soon as the JSON.SET command returns. Any subsequent query matching the indexed content will return the document.

Searching

To search for documents, use the FT.SEARCH commands. You can search any attribute mentioned in the SCHEMA.

Following our example, find the user called John:

FT.SEARCH userIdx '@name:(John)'
1) (integer) 1
2) "myDoc"
3) 1) "$"
   2) "{\"user\":{\"name\":\"John Smith\",\"tag\":\"foo,bar\",\"hp\":1000,\"dmg\":150}}"

Field projection

FT.SEARCH returns the whole document by default.

You can also return only a specific attribute (name for example):

FT.SEARCH userIdx '@name:(John)' RETURN 1 name
1) (integer) 1
2) "myDoc"
3) 1) "name"
   2) "\"John Smith\""

Projecting using JSON Path expressions

The RETURN parameter also accepts a JSON Path expression which lets you extract any part of the JSON document.

The following example returns the result of the JSON Path expression $.user.hp.

FT.SEARCH userIdx '@name:(John)' RETURN 1 $.user.hp
1) (integer) 1
2) "myDoc"
3) 1) "$.user.hp"
   2) "1000"

Note that the property name is the JSON expression itself: 3) 1) "$.user.hp"

Using the AS option, you can also alias the returned property.

FT.SEARCH userIdx '@name:(John)' RETURN 3 $.user.hp AS hitpoints
1) (integer) 1
2) "myDoc"
3) 1) "hitpoints"
   2) "1000"

Highlighting

You can highlight any attribute as soon as it is indexed using the TEXT type. For FT.SEARCH, you have to explicitly set the attribute in the RETURN and the HIGHLIGHT parameters.

FT.SEARCH userIdx '@name:(John)' RETURN 1 name HIGHLIGHT FIELDS 1 name TAGS '<b>' '</b>'
1) (integer) 1
2) "myDoc"
3) 1) "name"
   2) "\"<b>John</b> Smith\""

Aggregation with JSON Path expression

Aggregation is a powerful feature. You can use it to generate statistics or build facet queries. The LOAD parameter accepts JSON Path expressions. Any value (even not indexed) can be used in the pipeline.

This example loads two numeric values from the JSON document applying a simple operation.

FT.AGGREGATE userIdx '*' LOAD 6 $.user.hp AS hp $.user.dmg AS dmg APPLY '@hp-@dmg' AS points
1) (integer) 1
2) 1) "point"
   2) "850"

Current indexing limitations

JSON arrays can only be indexed in a TAG field.

It is only possible to index an array of strings or booleans in a TAG field. Other types (numeric, geo, null) are not supported.

It is not possible to index JSON objects.

To be indexed, a JSONPath expression must return a single scalar value (string or number).

If the JSONPath expression returns an object, it will be ignored.

However it is possible to index the strings in separated attributes.

Given the following document:

{
  "name": "Headquarters",
  "address": [
    "Suite 250",
    "Mountain View"
  ],
  "cp": "CA 94040"
}

Before you can index the array under the address key, you have to create two fields:

FT.CREATE orgIdx ON JSON SCHEMA $.address[0] AS a1 TEXT $.address[1] AS a2 TEXT
OK

You can now index the document:

JSON.SET org:1 $ '{"name": "Headquarters","address": ["Suite 250","Mountain View"],"cp": "CA 94040"}'
OK

You can now search in the address:

FT.SEARCH orgIdx "suite 250"
1) (integer) 1
2) "org:1"
3) 1) "$"
   2) "{\"name\":\"Headquarters\",\"address\":[\"Suite 250\",\"Mountain View\"],\"cp\":\"CA 94040\"}"

Index JSON strings and numbers as TEXT and NUMERIC

• You can only index JSON strings as TEXT, TAG, or GEO (using the right syntax).
• You can only index JSON numbers as NUMERIC.
• Boolean and NULL values are ignored.

SORTABLE not supported on TAG

FT.CREATE orgIdx ON JSON SCHEMA $.cp[0] AS cp TAG SORTABLE
(error) On JSON, cannot set tag field to sortable - cp

With hashes, you can use SORTABLE (as a side effect) to improve the performance of FT.AGGREGATE on TAGs. This is possible because the value in the hash is a string, such as "foo,bar".

With JSON, you can index an array of strings. Because there is no valid single textual representation of those values, there is no way for RediSearch to know how to sort the result.