querying.md

Querying

The query macro and where clause combine to give you full control over your query.

Where

Where is using a QueryBuilder that allows you to chain where clauses together to build up a complete query.

posts = Post.where(published: true, author_id: User.first!.id)

It supports different operators:

Post.where(:created_at, :gt, Time.local - 7.days)

Supported operators are :eq, :gteq, :lteq, :neq, :gt, :lt, :nlt, :ngt, :ltgt, :in, :nin, :like, :nlike

Alternatively, #where, #and, and #or accept a raw SQL clause, with an optional placeholder (? for MySQL/SQLite, $ for Postgres) to avoid SQL Injection.

# Example using Postgres adapter
Post.where(:created_at, :gt, Time.local - 7.days)
  .where("LOWER(author_name) = $", name)
  .where("tags @> '{"Journal", "Book"}') # PG's array contains operator

This is useful for building more sophisticated queries, including queries dependent on database specific features not supported by the operators above. However, clauses built with this method are not validated.

Order

Order is using the QueryBuilder and supports providing an ORDER BY clause:

Post.order(:created_at)

Direction

Post.order(updated_at: :desc)

Multiple fields

Post.order([:created_at, :title])

With direction

Post.order(created_at: :desc, title: :asc)

Group By

Group is using the QueryBuilder and supports providing an GROUP BY clause:

posts = Post.group_by(:published)

Multiple fields

Post.group_by([:published, :author_id])

Limit

Limit is using the QueryBuilder and provides the ability to limit the number of tuples returned:

Post.limit(50)

Offset

Offset is using the QueryBuilder and provides the ability to offset the results. This is used for pagination:

Post.offset(100).limit(50)

All

All is not using the QueryBuilder. It allows you to directly query the database using SQL.

When using the all method, the selected fields will match the fields specified in the model unless the select macro was used to customize the SELECT.

Always pass in parameters to avoid SQL Injection. Use a ? in your query as placeholder. Checkout the Crystal DB Driver for documentation of the drivers.

Here are some examples:

posts = Post.all("WHERE name LIKE ?", ["Joe%"])
if posts
  posts.each do |post|
    puts post.name
  end
end

# ORDER BY Example
posts = Post.all("ORDER BY created_at DESC")

# JOIN Example
posts = Post.all("JOIN comments c ON c.post_id = post.id
                  WHERE c.name = ?
                  ORDER BY post.created_at DESC",
                  ["Joe"])

Customizing SELECT

The select_statement macro allows you to customize the entire query, including the SELECT portion. This shouldn't be necessary in most cases, but allows you to craft more complex (i.e. cross-table) queries if needed:

class CustomView < Granite::Base
  connection pg

  column id : Int64, primary: true
  column articlebody : String
  column commentbody : String

  select_statement <<-SQL
    SELECT articles.articlebody, comments.commentbody
    FROM articles
    JOIN comments
    ON comments.articleid = articles.id
  SQL
end

You can combine this with an argument to all or first for maximum flexibility:

results = CustomView.all("WHERE articles.author = ?", ["Noah"])

Note - the column order does matter, and you should match your SELECT query to have the columns in the same order they are in the database.

Exists?

The exists? class method returns true if a record exists in the table that matches the provided id or criteria, otherwise false.

If passed a Number or String, it will attempt to find a record with that primary key. If passed a Hash or NamedTuple, it will find the record that matches that criteria, similar to find_by.

# Assume a model named Post with a title field
post = Post.new(title: "My Post")
post.save
post.id # => 1

Post.exists? 1 # => true
Post.exists? {"id" => 1, :title => "My Post"} # => true
Post.exists? {id: 1, title: "Some Post"} # => false

The exists? method can also be used with the query builder.

Post.where(published: true, author_id: User.first!.id).exists?
Post.where(:created_at, :gt, Time.local - 7.days).exists?