Chris Mendez in For Developers, Ruby

Rails: Querying the model

Thanks to some metaprogramming magic, whenever you create a column within a table, you get a free find_by_[name of column] method.

Create a new Friend model with a name and address:

rails g model Friend name:string address:string  
rails db:migrate  

find_by_[name of column]

If you use Rails Command Line to create a model, then you get this method for free.

Query a friend by their name:

f = Friend.find_by_name("name of friend")  

Query a friend by their address:

f = Friend.find_by_address("5555 Disney Ave, Los Angeles, CA")  

Query a friend by their database ID:

# f = Friend.find(1)
f = Friend.find(params[:id])  

Query everyone in the database:

f = Friend.all  

ILIKE

You also get a LIKE operator for situations where you only have a partial address:

a = Friend.where("address ILIKE ?", "%partial address%")  

SQL Only

This is only for very specific circumstances but you can also create a raw SQL command.

Friend.find_by_sql "enter your specific SQL query"  

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