Query Builder

Query Builder allows you to build and compose Ecto queries based on data.

User
|> QueryBuilder.where(firstname: "John")
|> QueryBuilder.where([{:age, :gt, 30}, city: "Anytown"])
|> QueryBuilder.order_by(lastname: :asc)
|> QueryBuilder.preload([:role, authored_articles: :comments])
|> Repo.all()

This allows writing queries more concisely, without having to deal with bindings and macros.

Its primary goal is to allow Context functions to receive a set of filters and options:

Blog.list_articles(preload: :comments, order_by: [title: :asc])
Blog.list_articles(preload: [:category, comments: :user])

This avoids having to create many different functions in the Context for every combination of filters and options, or to create one general function that does too much to satisfy all the consumers.

The calling code (e.g. the Controllers), can now retrieve the list of articles with different options. In some part of the application, the category is needed; in other parts it is not; sometimes the articles must be sorted based on their title; other times it doesn't matter, etc.

See QueryBuilder.from_list/2 below.

Examples

User
|> QueryBuilder.where(firstname: "John")
|> QueryBuilder.where([{:age, :gt, 30}, city: "Anytown"])
|> QueryBuilder.order_by(lastname: :asc)
|> QueryBuilder.preload([:role, authored_articles: :comments])
|> Repo.all()

Filtering on associations is supported:

User
|> QueryBuilder.where(:role, name@role: "admin")
|> Repo.all()

User
|> QueryBuilder.where([role: :permissions], name@permissions: "delete")
|> Repo.all()

Article
|> QueryBuilder.where(:author, id@author: author_id)
|> QueryBuilder.where([:author, :comments], {:logged_at@author, :lt, :inserted_at@comments})
|> QueryBuilder.preload(:comments)
|> Repo.all()

Usage

Add use QueryBuilder in your schema:

defmodule MyApp.User do
  use Ecto.Schema
  use QueryBuilder

  schema "users" do
    # code
  end

  # code
end

You may also specify the schema's associations to QueryBuilder in order to remedy some limitations when building queries:

defmodule MyApp.User do
  use Ecto.Schema
  use QueryBuilder, assoc_fields: [:role, :articles]

  schema "users" do
    # code
    belongs_to :role, MyApp.Role
    has_many :articles, MyApp.Article
  end

  # code
end

Currently supported operations are:

QueryBuilder.where/2

QueryBuilder.where(query, firstname: "John")

QueryBuilder.where/3

QueryBuilder.where(query, [role: :permissions], name@permissions: :write)

QueryBuilder.order_by/2

QueryBuilder.order_by(query, lastname: :asc, firstname: :asc)

QueryBuilder.order_by/3

QueryBuilder.order_by(query, :articles, title@articles: :asc)

QueryBuilder.preload/2

QueryBuilder.preload(query, [role: :permissions, articles: [:stars, comments: :user]])

QueryBuilder.join/3

QueryBuilder.join(query, :articles, :left)

QueryBuilder.from_list/2

QueryBuilder.from_list(query, [
  where: [name: "John", city: "Anytown"],
  preload: [articles: :comments]
])

The QueryBuilder.from_list/2 function was the main motivation behind the writing of this library. As explained above, it allows to add querying options to the Context functions. Example:

defmodule MyApp.Blog do
  alias MyApp.Blog.Article

  def get_article_by_id(id, opts \\ []) do
    QueryBuilder.where(Article, id: id)
    |> QueryBuilder.from_list(opts)
    |> Repo.one!()
  end
end

The function can now be called as follows (for instance, from a Controller):

Blog.get_article_by_id(id, preload: [:comments])

Blog.get_article_by_id(id, preload: [:likes])

Blog.get_article_by_id(
  id,
  order_by: {:comments, inserted_at@comments: :desc},
  preload: [comments: :user]
)

Installation

Add query_builder for Elixir as a dependency in your mix.exs file:

def deps do
  [
    {:query_builder, "~> 0.9.0"}
  ]
end

HexDocs

HexDocs documentation can be found at https://hexdocs.pm/query_builder.