regex¶
Definition¶
regex
¶regex
interprets thequery
field as a regular expression.regex
is a term-level operator, meaning that thequery
field isn't analyzed.TipSee also:NoteThe regular expression language available to the
regex
operator is a limited subset of the PCRE library.For detailed information, see the Class RegExp documentation.
Syntax¶
regex
has the following syntax:
1 { 2 $search: { 3 "index": <index name>, // optional, defaults to "default" 4 "regex": { 5 "query": "<search-string>", 6 "path": "<field-to-search>", 7 "allowAnalyzedField": <boolean>, 8 "score": <options> 9 } 10 } 11 }
Options¶
regex
uses the following terms to construct a query:
Field | Type | Description | Necessity | Default |
---|---|---|---|---|
query | string or array of strings | String or strings to search for. | yes | |
path | string or array of strings | Indexed field or fields to search. You can also specify a
wildcard path to search. See path construction for more information. | yes | |
allowAnalyzedField | boolean | Must be set to true if the query is run against an analyzed
field. | no | false |
score | object | Modify the score assigned to matching search term results. Options are:
| no |
Behavior¶
regex
is a term-level operator, meaning that the query
field is
not analyzed. Regular expression searches work well with the
keyword analyzer, because it indexes
fields one word at a time. To do a case-sensitive search, do not use
the default analyzer, standard analyzer,
because the standard
analyzer lower cases all terms. Specify a
different analyzer instead.
It is possible to use the regex
operator to perform searches on an
analyzed field by setting the allowAnalyzedField
option to
true
, but you may get unexpected results.
Searching for *Star Trek*
on a field indexed with the
keyword
analyzer finds all documents in which the field contains
the string Star Trek
in any context. Searching for *Star
Trek*
on a field indexed with the standard analyzer finds nothing, because there is a space
between Star
and Trek
, and the index contains no spaces.
Lucene Regular Expression Behavior¶
The Atlas Search regex
operator uses the Lucene regular expression engine,
which differs from Perl Compatible Regular Expressions.
Reserved characters¶
The following characters are reserved as operators when used in regular expressions:
. ? + * | { } [ ] ( ) " \ @
To use any of the above characters literally in a matching expression,
precede it with a \
character.
who\?
matches "who?"
When using the escape character in mongosh
or with a driver, you must use a double backslash before the character to be escaped.
To create a wildcard expression which searches for any string containing a literal asterisk in an aggregation pipeline, use the following expression:
"*\\**"
The first and last asterisks act as wildcards which match any
characters, and the \\*
matches a literal asterisk.
Use the following expression to escape a literal backslash:
"*\\\*"
Supported Operators¶
Operator | Description | Example |
---|---|---|
. | Matches any character. | x.z matches "xyz", "xaz", etc. |
? | The preceding character is optional and matches if it occurs no more than
once. | xyz? matches "xy" and "xyz" |
+ | The preceding character matches if it occurs one or more times. | xy+ matches "xy", "xyy", "xyyy", etc. |
* | The preceding character matches if it occurs any number of times. | xyz* matches "xy", "xyz", "xyzz", etc. |
{<number>} | The preceding character matches if it occurs exactly <number> times. | xyz{3} matches "xyzzz" |
| | The OR operator. The expression matches if the longer of the two
patterns on either side of the | operator matches. | abc|xyz matches "abc" or "xyz" |
() | Characters inside parentheses are treated as a single unit for matching
purposes. | xyz(abc)[2] matches "xyzabcabc" |
[] | Match any of the characters inside the square brackets. Adding a ^
to the beginning matches any character except those within the square
brackets. | [xyz] matches "x", "y", and "z"
[^abc] matches any character except "a", "b", or "c" |
Unsupported Operators¶
regex
does not support the anchor operators ^
and $
.
Examples¶
The following examples use the movies
collection in the
sample_mflix
database with a custom index definition that uses the
keyword analyzer. If you have the
sample dataset on your cluster, you
can create an Atlas Search index on the movies
collection and run the
example queries on your cluster.
If you've already loaded the sample dataset, follow the Get Started with Atlas Search tutorial to create an index definition and run Atlas Search queries.
Index Definition¶
The following index definition indexes the title
field in the
movies
collection with the
keyword analyzer:
1 { 2 "mappings": { 3 "fields": { 4 "title": { 5 "analyzer": "lucene.keyword", 6 "type": "string" 7 } 8 } 9 } 10 }
The following example searches all title
fields for movie titles
that end with the word Seattle
. The (.*)
regular expression
matches any number of characters.
1 db.movies.aggregate([ 2 { 3 "$search": { 4 "regex": { 5 "path": "title", 6 "query": "(.*) Seattle" 7 } 8 } 9 }, 10 { 11 $project: { 12 "_id": 0, 13 "title": 1 14 } 15 } 16 ])
The above query returns the following results:
{ "title" : "Sleepless in Seattle" } { "title" : "Battle in Seattle" }
The following example uses the regular expression [0-9]{2} (.){4}s
to find movie titles which begin with a 2-digit number followed by a
space, and end with a 5-letter word ending in s
.
1 db.movies.aggregate([ 2 { 3 "$search": { 4 "regex": { 5 "path": "title", 6 "query": "[0-9]{2} (.){4}s" 7 } 8 } 9 }, 10 { 11 $project: { 12 "_id": 0, 13 "title": 1 14 } 15 } 16 ])
The above query returns the following results:
{ "title" : "20 Dates" } { "title" : "25 Watts" } { "title" : "21 Grams" } { "title" : "13 Lakes" } { "title" : "18 Meals" } { "title" : "17 Girls" } { "title" : "16 Acres" } { "title" : "26 Years" } { "title" : "99 Homes" } { "title" : "45 Years" }