The following examples use a collection called products with the following documents. The $regex implementation, for example, is not collation-aware and hence cannot use case-insensitive indexes. Regular expression queries that are case insensitive can’t leverage indexes efficiently. After matching the prefix, /^a/ can stop searching. If a suitable index exists, all of these expressions use it nevertheless, /^a.*/ and /^a.*$/ are slower. For example, the regex /^abc.*/ will be optimized by only matching against index values that begin with abc.įurthermore, while /^a/, /^a.*/, and /^a.*$/ all match comparable strings, their performance is different. If a regular expression begins with a caret ( ^) or a left anchor ( \A), followed by a string of simple symbols, it is called a prefix expression. This enables MongoDB to create a range from the prefix and only match against index values within that range. More optimization is possible if the regular expression has a prefix expression, which indicates that all potential matches begin with the exact string. If the field has an index, MongoDB checks the regular expression against the values in the index, which can be faster than a collection scan for case-sensitive regular expression queries. pattern/) but not with the $regex operator expressions. In version 4.0.6 and earlier, you could use the $not operator with regular expression objects (i.e. Consider the following example.ĭb.inventory.find ( ) Only JavaScript regular expression objects (i.e., /pattern/) can be used to incorporate a regular expression in the $in query expression. The $regex operator doesn’t support the global search modifier g. ) to match any character, including newlines. It will require $regex with $options syntax s It allows the dot character (. early and often: Identify common query patterns using MMS, Compass GUI. The x option does not affect how the VT character is handled (i.e., code 11). An expert's guide to building fault-tolerant MongoDB applications Alex Giamas. White space characters might not appear within special character sequences in a pattern this only pertains to data characters. It also ignores characters in the middle and includes an unescaped hash/pound ( #) character and the following newline, allowing you to add comments in complex patterns. x All white space characters in the $regex pattern are ignored unless they are escaped or included in a character class. The m option has no effect if the pattern has no anchors or if the string value contains no newline characters (e.g. m For strings with multi-line values, match at the beginning or end of each line for patterns that include anchors such as ^ at the start and $ at the end. Option Description Syntax Restrictions i Case insensitive to match upper and lower cases. The user can use regular expressions with the following.
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