HOW TO : Search for a record in MongoDB based on length

Quick entry for my own records.

MongoDB is one of the popular open source document database that is part of the nosql movement. One of the applications we deployed at work uses MongoDB as an internal storage engine. We ran into an issue where MongoDB was trying to replicate data to MySQL and the replication stopped because of a size mismatch for an object between MongoDB and MySQL. Essentially MongoDB was trying to insert a record into MySQL that was larger than the defined length.

Here is the query we used to find the culprit objects. We used the awesome Robomongo client to connect to the MongoDB instance.

[code]db.some_table_to_search.find({$where:"this.some_column_to_search.length > 40"})[/code]

Breaking down the command

db -> Specifies the database you are trying to search

some_table_to_search -> Specifie the table you are trying to search

some_column_to_search -> Specified the particular column you are trying to search.

In this specific example, we were looking for entries longer than 40 characters for this column.

If you come from the traditional RDBMS world, here is a link from MongoDB comparing terminology between RDBMS and MongoDB.

http://docs.mongodb.org/manual/reference/sql-comparison/

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