Method: ROM::SQL::Relation::Reading#select

Defined in:: lib/rom/sql/relation/reading.rb

#select(columns) ⇒ `Relation` #select(attributes) ⇒ `Relation` #select(&block) ⇒ `Relation` #select(*columns, &block) ⇒ `Relation` Also known as: project

Select specific columns for select clause

Overloads:

#select(*columns) ⇒ Relation

Project relation using column names
Examples:

using column names
```
users.select(:id, :name).first
# {:id => 1, :name => "Jane"}
```
Parameters:
- columns (Array<Symbol>) —
  
  A list of column names
#select(*attributes) ⇒ Relation

Project relation using schema attributes
Examples:

using attributes
```
users.select(:id, :name).first
# {:id => 1, :name => "Jane"}
```
using schema
```
users.select(*schema.project(:id)).first
# {:id => 1}
```
Parameters:
- columns (Array<SQL::Attribute>) —
  
  A list of schema attributes

#select(&block) ⇒ Relation

Project relation using projection DSL

Examples:

using attributes

users.select { id.as(:user_id) }
# {:user_id => 1}

users.select { [id, name] }
# {:id => 1, :name => "Jane"}

using SQL functions

users.select { string::concat(id, '-', name).as(:uid) }.first
# {:uid => "1-Jane"}

#select(*columns, &block) ⇒ Relation

Project relation using column names and projection DSL
Examples:

using attributes
```
users.select(:id) { int::count(id).as(:count) }.group(:id).first
# {:id => 1, :count => 1}

users.select { [id, name] }
# {:id => 1, :name => "Jane"}
```
Parameters:
- columns (Array<SQL::Attribute>) —
  
  A list of schema attributes

Returns:

(Relation)



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# File 'lib/rom/sql/relation/reading.rb', line 215

def select(*args, &block)
  schema.project(*args, &block).(self)
end