![]() In the query below u is a binding and u.age is a field access using this binding. This is done inside from and join clauses. On the left side of in we specify the query bindings. ![]() In any case, regardless if a schema has been given or not, Ecto queries are always composable thanks to its binding system. For now, we know such protocols is implemented for both atoms (like User) and strings (like “users”). ![]() The difference is that, instead of passing a schema like Weather on the right side of in, we passed the query itself.Īny value can be used on the right-side of in as long as it implements the Ecto.Queryable protocol. Query = from u in User, where: u.age > 18Ĭomposing queries uses the same syntax as creating a query. For example, the query above can actually be defined in two parts: # Create a query Repo.all(from u in User, where: u.age > ^age)įor this reason, we will use schemas on the remaining examples but remember Ecto does not require them in order to write queries. Repo.all(from u in User, where: u.age > ^age, select: u.name)Īnother advantage of using schemas is that we no longer need to specify the select option in queries, as by default Ecto will retrieve all fields specified in the schema: age = "18" In such cases, Ecto will analyze your queries and automatically cast the interpolated “age” when compared to the u.age field, as long as the age field is defined with type :integer in your schema: age = "18" To avoid the repetition of always specifying the types, you may define an Ecto.Schema. In the example above, Ecto will cast the age to type integer. When interpolating values, you may want to explicitly tell Ecto what is the expected type of the value being interpolated: age = "18" Where: u.age > ^age and u.height > ^(height_ft * 3.28), Interpolation and castingĮxternal values and Elixir expressions can be injected into a query expression with ^: def with_minimum(age, height_ft) do Arrays:, ~w(interpolate words)Īll other types and dynamic values must be passed as a parameter using interpolation as explained below.Strings: "foo bar", ~s(this is a string).Besides the operations listed there, the following literals are supported in queries: You can find the full list of operations in. In the query below, for example, we use u.age to access a field, the > comparison operator and the literal 0: query = from u in "users", where: u.age > 0, select: u.name Query expressionsĮcto allows a limited set of expressions inside queries. In the example above, we are directly querying the “users” table from the database. Let’s see a sample query: # Imports only from/2 of Ecto.Query Most examples will use the keyword-based syntax, the macro one will be explored in later sections. Ecto queries come in two flavors: keyword-based and macro-based. , % Friends.Queries are used to retrieve and manipulate data from a repository (see Ecto.Repo). Below, we’ll get the movie with an ID of 1: iex> alias Friends. It returns nil if no such record is found. It returns a struct describing the record found, if any. This function requires two arguments: a “queryable” data structure and the ID of a record to retrieve from the database. We can use the Repo.get/3 function to fetch a record from the database given its ID. We can perform simple queries directly against our Friends.Repo with the help of a handful of functions. Recall that a “repository” in Ecto maps to a datastore such as our Postgres database.Īll communication to the database will be done using this repository. In this lesson, we’ll continue building off the Friends app and the movie-cataloguing domain we set up in the previous lesson.
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