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MongoDB how to use regex, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

Part1: write at the front

Friends who use MySQL or other relational databases know that the use of fuzzy queries is similar to:

SELECT * FROM products WHERE sku like "789"

The regex in MongoDB introduced in this article implements a similar function. Regex enables you to use regular expressions in your queries. This article will show you how to use regex in MongoDB with simple examples.

Part2: usage

When using $regex, there are several uses:

{: {$regex: / pattern/, $options:''}} {: {$regex: 'pattern', $options:''} {: {$regex: / pattern/}}

The meaning of the option parameter:

Option meaning usage requirement I case insensitive m

Anchors are used in query matching, such as ^ (for the beginning) and $(for the end), and the string after the match\ n

X

Ignore all white space characters

Require $regex to share with $option s to allow dot characters (.) to match all characters, including newline characters. Require $regex to be shared with $option

Actual combat

Usage in Part1:$in

To include regular expressions in a $in query, you can only use the JavaScript regular expression object (that is, / pattern /). For example:

{name: {$in: [/ ^ acme/i, / ^ ack/]}}

Warning: warning that $regex operator expressions cannot be used in $in.

Part2: implicit and usage

To include regular expressions in comma-separated query conditions, use the $regex operator. For example:

{name: {$regex: / acme.*corp/i, $nin: ['acmeblahcorp']}} {name: {$regex: / acme.*corp/, $options:' acmeblahcorp', $nin: ['acmeblahcorp']}} {name: {$regex:' acme.*corp', $options: 'nin: [' acmeblahcorp']}

Part3:x and s option

To use the x option or the s option, $regex is required to be used with $option. For example, to specify the I and s options, you must use $options to do the following:

{name: {$regex: / acme.*corp/, $options: "si"} {name: {$regex: 'acme.*corp', $options: "si"}

Part4: the use of indexes

For case-sensitive regular expression queries, if the field has an index, MongoDB matches the regular expression to the value in the index, which is faster than a full table scan. If the regular expression is a "prefix expression", the query speed can be optimized and the query results will start with the same string.

Regular expressions should also conform to the leftmost prefix principle; for example, the regular expression / ^ abc.*/ will be optimized by matching only index values that start with abc.

Warning: warning

1. Although / ^ a _ gray / matches the equivalent string, their performance is not the same. If there is a corresponding index, all of these expressions use the index; however, / ^ a.indexes / and / ^ a.indexes examples / are slower. This is because / ^ a / can stop scanning after matching the prefix.

two。 Case-insensitive regular expression queries usually cannot use indexes, and $regex cannot use case-insensitive indexes.

Part5: instance

In a collection of goods, the following are stored

{"_ id": 100, "sku": "abc123", "description": "Single line description."} {"_ id": 101, "sku": "abc789", "description": "First line\ nSecond line"} {"_ id": 102, "sku": "xyz456", "description": "Many spaces before line"} {"_ id": 103, "sku": "xyz789", "description": "Multiple\ nline description"}

If you want to execute a query against the products collection of the item, the scope is that the content in the sku column ends with 789:

Db.products.find ({sku: {$regex: / 789 $/}})

Combined with the understanding of MySQL, the above query looks like this SQL in MySQL:

SELECT * FROM products WHERE sku like "789"

If you want to query sku with the beginning of abc and ABC, and ignore case when matching, you can use the I option:

Db.products.find ({sku: {$regex: / ^ ABC/i}}),

The query results are as follows:

{"_ id": 100, "sku": "abc123", "description": "Single line description."} {"_ id": 101,101, "sku": "abc789", "description": "First line\ nSecond line"}

The use of Part6:m

If you want to include S in the query description, and to match the S after / n, you need to add the m option.

Db.products.find ({description: {$regex: / ^ Smax, $options:'m'}})

The result returned is:

{"_ id": 100, "sku": "abc123", "description": "Single line description."} {"_ id": 101,101, "sku": "abc789", "description": "First line\ nSecond line"}

If you do not add the m option, the result returned is as follows:

{"_ id": 100, "sku": "abc123", "description": "Single line description."}

If an anchor such as ^ is not used, all results will be returned:

Db.products.find ({description: {$regex: / S /}}) {"_ id": 100, "sku": "abc123", "description": "Single line description."} {"_ id": 101, "sku": "abc789", "description": "First line\ nSecond line"}

The use of Part7:s

If you use the s option to execute the query, you will have a comma. Matches all characters, including newline characters. The following query starts with m in the description column, followed by the result of the line string:

Db.products.find ({description: {$regex: / m.options: 'si'}}) {"_ id": 102, "sku": "xyz456", "description": "Many spaces before line"} {"_ id": 103, "sku": "xyz789", "description": "Multiple\ nline description"}

If s is not included, it returns:

{"_ id": 102,102, "sku": "xyz456", "description": "Many spaces before line"}

The use of Part8:x

The following example uses the x option to ignore spaces and comments, denotes comments with #, and ends with\ nin the match pattern:

Var pattern = "abc # category code\ n123 # item number" db.products.find ({sku: {$regex: pattern, $options: "x"}})

The result of the query is:

{"_ id": 100, "sku": "abc123", "description": "Single line description."}

As you can see, it ignores the spaces of abc and # category and the spaces of # category and code, and the query actually executed is the result of sku being abc123.

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