Merge branch 'dp_docs'

Closes rails#6697

Author: carlosantoniodasilva

activerecord/lib/active_record/relation/query_methods.rb

@@ -194,10 +194,102 @@ def bind!(value)
       self
     end
 
+    # Returns a new relation, which is the result of filtering the current relation
+    # according to the conditions in the arguments.
+    #
+    # #where accepts conditions in one of several formats. In the examples below, the resulting
+    # SQL is given as an illustration; the actual query generated may be different depending
+    # on the database adapter.
+    #
+    # === string
+    #
+    # A single string, without additional arguments, is passed to the query
+    # constructor as a SQL fragment, and used in the where clause of the query.
+    #
+    #    Client.where("orders_count = '2'")
+    #    # SELECT * from clients where orders_count = '2';
+    #
+    # Note that building your own string from user input may expose your application
+    # to injection attacks if not done properly. As an alternative, it is recommended
+    # to use one of the following methods.
+    #
+    # === array
+    #
+    # If an array is passed, then the first element of the array is treated as a template, and
+    # the remaining elements are inserted into the template to generate the condition.
+    # Active Record takes care of building the query to avoid injection attacks, and will
+    # convert from the ruby type to the database type where needed. Elements are inserted
+    # into the string in the order in which they appear.
+    #
+    #   User.where(["name = ? and email = ?", "Joe", "[email protected]"])
+    #   # SELECT * FROM users WHERE name = 'Joe' AND email = '[email protected]';
+    #
+    # Alternatively, you can use named placeholders in the template, and pass a hash as the
+    # second element of the array. The names in the template are replaced with the corresponding
+    # values from the hash.
+    #
+    #   User.where(["name = :name and email = :email", { name: "Joe", email: "[email protected]" }])
+    #   # SELECT * FROM users WHERE name = 'Joe' AND email = '[email protected]';
+    #
+    # This can make for more readable code in complex queries.
+    #
+    # Lastly, you can use sprintf-style % escapes in the template. This works slightly differently
+    # than the previous methods; you are responsible for ensuring that the values in the template
+    # are properly quoted. The values are passed to the connector for quoting, but the caller
+    # is responsible for ensuring they are enclosed in quotes in the resulting SQL. After quoting,
+    # the values are inserted using the same escapes as the Ruby core method <tt>Kernel::sprintf</tt>.
+    #
+    #   User.where(["name = '%s' and email = '%s'", "Joe", "[email protected]"])
+    #   # SELECT * FROM users WHERE name = 'Joe' AND email = '[email protected]';
+    #
+    # If #where is called with multiple arguments, these are treated as if they were passed as
+    # the elements of a single array.
+    #
+    #   User.where("name = :name and email = :email", { name: "Joe", email: "[email protected]" })
+    #   # SELECT * FROM users WHERE name = 'Joe' AND email = '[email protected]';
+    #
+    # When using strings to specify conditions, you can use any operator available from
+    # the database. While this provides the most flexibility, you can also unintentionally introduce
+    # dependencies on the underlying database. If your code is intended for general consumption,
+    # test with multiple database backends.
+    #
+    # === hash
+    #
+    # #where will also accept a hash condition, in which the keys are fields and the values
+    # are values to be searched for.
+    #
+    # Fields can be symbols or strings. Values can be single values, arrays, or ranges.
+    #
+    #    User.where({ name: "Joe", email: "[email protected]" })
+    #    # SELECT * FROM users WHERE name = 'Joe' AND email = '[email protected]'
+    #
+    #    User.where({ name: ["Alice", "Bob"]})
+    #    # SELECT * FROM users WHERE name IN ('Alice', 'Bob')
+    #
+    #    User.where({ created_at: (Time.now.midnight - 1.day)..Time.now.midnight })
+    #    # SELECT * FROM users WHERE (created_at BETWEEN '2012-06-09 07:00:00.000000' AND '2012-06-10 07:00:00.000000')
+    #
+    # === Joins
+    #
+    # If the relation is the result of a join, you may create a condition which uses any of the
+    # tables in the join. For string and array conditions, use the table name in the condition.
+    #
+    #    User.joins(:posts).where("posts.created_at < ?", Time.now)
+    #
+    # For hash conditions, you can either use the table name in the key, or use a sub-hash.
+    #
+    #    User.joins(:posts).where({ "posts.published" => true })
+    #    User.joins(:posts).where({ :posts => { :published => true } })
+    #
+    # === empty condition
+    #
+    # If the condition returns true for blank?, then where is a no-op and returns the current relation.
     def where(opts, *rest)
       opts.blank? ? self : spawn.where!(opts, *rest)
     end
 
+    # #where! is identical to #where, except that instead of returning a new relation, it adds
+    # the condition to the existing relation.
     def where!(opts, *rest)
       references!(PredicateBuilder.references(opts)) if Hash === opts