Active Record allows you to execute SQL commands using Ruby. This guide cuts through the fluff to provide a simple reference for some common Active Record queries. For each query, you’ll find the SQL equivalent and a brief description of what it returns, making it easy to see how the methods map to SQL commands.

find

• SQL Equivalent: SELECT * FROM model WHERE (model.id = :id)
• Returns: the record with the specific ID.

take

• SQL Equivalent: SELECT * FROM model LIMIT 1
• Returns: the record without any ordering

first

• SQL Equivalent: SELECT * FROM model ORDER BY model.id ASC LIMIT 1
• Returns: the record with the first primary key that exists

last

• SQL Equivalent: SELECT * FROM model ORDER BY model.id DESC LIMIT 1
• Returns: the record with the last primary key that exists

find_by

• SQL Equivalent: SELECT * FROM model WHERE (model.parameter = 'foo') LIMIT 1
• Returns: the first record matching the condition

This is not meant to be an exhaustive guide.
For more information, see the Rails Guides: Active Record Query Interface.

 
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