Join: c in Comment, where: c.post_id = p.id When using joins, the bindings should be matched in the order they are specified: # Create a query This is important because it allows developers to compose queries without caring about the bindings used in the initial query. For example, the query above could also be written as: query = from q in query, select: q.city For example to further narrow-down above query we again need to tell Ecto what bindings to expect: query = from u in query, select: u.cityīindings in Ecto are positional, and the names do not have to be consistent between input and refinement queries. When composing queries you must specify bindings again for each refinement query. query = from u in User, where: u.age > 18īindings are not exposed from the query. 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. Queries are used to retrieve and manipulate data from a repository (see Ecto.Repo).
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