Sequel offers unparalleled flexibility when it comes to filtering records. You can specify your conditions as a custom string, as a string with parameters, as a hash of values to compare against, or as ruby code that Sequel translates into SQL expressions.
If you wish to write your SQL by hand, you can just supply it to the dataset’s filter method:
items.filter('x < 10').sql #=> "SELECT * FROM items WHERE x < 10"
In order to prevent SQL injection, you can replace literal values with question marks and supply the values as additional arguments:
items.filter('category = ?', 'ruby').sql #=> "SELECT * FROM items WHERE category = 'ruby'"
Sequel also allows you to specify functions by using the Symbol#sql_function method (and the Symbol#[] method on ruby 1.8):
items.literal(:avg.sql_function(:price)) #=> "avg(price)"
If you just need to compare records against values, you can supply a hash:
items.filter(:category => 'ruby').sql #=> "SELECT * FROM items WHERE (category = 'ruby')"
Sequel can check for null values:
items.filter(:category => nil).sql #=> "SELECT * FROM items WHERE (category IS NULL)"
Or compare two columns:
items.filter(:x => :some_table__y).sql #=> "SELECT * FROM items WHERE (x = some_table.y)"
And also compare against multiple values:
items.filter(:category => ['ruby', 'perl']).sql #=> "SELECT * FROM items WHERE (category IN ('ruby', 'perl'))"
Ranges (both inclusive and exclusive) can also be used:
items.filter(:price => 100..200).sql #=> "SELECT * FROM items WHERE (price >= 100 AND price <= 200)" items.filter(:price => 100...200).sql #=> "SELECT * FROM items WHERE (price >= 100 AND price < 200)"
Sequel allows you to use ruby expressions directly in the call to filter:
items.filter(:price * 2 < 50).sql #=> "SELECT * FROM items WHERE ((price * 2) < 50)
This works for the standard inequality and arithmetic operators (though you can’t use the inequality operators directly on a symbol in ruby 1.9):
items.filter(:price + 100 < 200).sql #=> "SELECT * FROM items WHERE ((price + 100) < 200) items.filter(:price - 100 > 200).sql #=> "SELECT * FROM items WHERE ((price - 100) > 200) items.filter(:price * 100 <= 200).sql #=> "SELECT * FROM items WHERE ((price * 100) <= 200) items.filter(:price / 100 >= 200).sql #=> "SELECT * FROM items WHERE ((price / 100) >= 200)
You use the overloaded bitwise and (&) and or (|) operators to combine expressions:
items.filter((:price + 100 < 200) & (:price * 100 <= 200)).sql #=> "SELECT * FROM items WHERE (((price + 100) < 200) AND ((price * 100) <= 200)) items.filter((:price - 100 > 200) | (:price / 100 >= 200)).sql #=> "SELECT * FROM items WHERE (((price - 100) > 200) OR ((price / 100) >= 200))
To filter by equality, you use the standard hash, which can be combined with other operators:
items.filter({:category => 'ruby'} & (:price + 100 < 200)).sql #=> "SELECT * FROM items WHERE ((category = 'ruby') AND ((price + 100) < 200))"
This works with other hash values, such as arrays and ranges:
items.filter({:category => ['ruby', 'other']} | (:price - 100 > 200)).sql #=> "SELECT * FROM items WHERE ((category IN ('ruby', 'other')) OR ((price - 100) <= 200))" items.filter({:price => (100..200)} & :active).sql #=> "SELECT * FROM items WHERE ((price >= 100 AND price <= 200) AND active)"
You can use the negation operator (~) in most cases:
items.filter(~{:category => 'ruby'}).sql #=> "SELECT * FROM items WHERE (category != 'ruby')" items.filter{~:active}.sql #=> "SELECT * FROM items WHERE NOT active" items.filter(~(:price / 100 >= 200)).sql #=> "SELECT * FROM items WHERE ((price / 100) < 200)
You can also compare against other columns:
items.filter{|o| o.credit > :debit}.sql #=> "SELECT * FROM items WHERE (credit > debit)
Or against SQL functions:
items.filter{|o| :price - 100 < o.max(:price)}.sql #=> "SELECT * FROM items WHERE ((price - 100) < max(price))"
You can search SQL strings using the like method:
items.filter(:name.like('Acme%')).sql #=> "SELECT * FROM items WHERE (name LIKE 'Acme%')"
You can specify a Regexp as a like argument, but this will probably only work on PostgreSQL and MySQL:
items.filter(:name.like(/Acme.*/)).sql #=> "SELECT * FROM items WHERE (name ~ 'Acme.*')"
Like can also take more than one argument:
items.filter(:name.like('Acme%', /Beta.*/)).sql #=> "SELECT * FROM items WHERE ((name LIKE 'Acme%') OR (name ~ 'Beta.*'))"
You can concatenate SQL strings using Array#sql_string_join:
items.filter([:name, :comment].sql_string_join.like('%acme%')).sql #=> "SELECT * FROM items WHERE ((name || comment) LIKE 'Acme%')"
Array#sql_string_join also takes a join argument:
items.filter([:name, :comment].sql_string_join(' ').like('%acme%')).sql #=> "SELECT * FROM items WHERE ((name || ' ' || comment) LIKE 'Acme%')"
One of the best features of Sequel is the ability to use datasets as sub-queries. Sub-queries can be very useful for filtering records, and many times provide a simpler alternative to table joins. Sub-queries can be used in all forms of filters:
refs = consumer_refs.filter(:logged_in).select(:consumer_id) consumers.filter(:id => refs).sql #=> "SELECT * FROM consumers WHERE (id IN (SELECT consumer_id FROM consumer_refs WHERE logged_in))"
Note that if you compare against a sub-query, you must select a single column in the sub-query.
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