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Work occasionally according to the length of the string field to filter some data, this time may use regular expressions, you can also use mongodb $where, regular expressions in different languages, the correct way to write different, here to record.

If you look for data with a comment field string length greater than 10, the mongodb command line is written as follows:

Where is written as follows:

Find ({"comment": {"$exists": true}, "$where": "this.comment.length > 10"})

How to write a regular expression:

Find ({"comment": {"$regex": / ^. {10,} $/}})

It is written as follows in go language:

Where is written as follows:

Collection.Find (bson.M {"comment": bson.M {"$exists": true}, "$where": "this.comment.length > 10"})

How to write a regular expression:

Collection.Find (bson.M {"comment": bson.M {"$exists": true, "$regex": bson.RegEx {`^. {10,} $`, ""})

Other conditions are regular:

^. {n ·m} $n

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