¿Cómo puedo consultar una base de datos en Ecto?

How can I query a database in Ecto?

Recall that a “repository” in Ecto maps to a datastore such as our Postgres database. All communication to the database will be done using this repository. We can perform simple queries directly against our Friends.Repo with the help of a handful of functions. We can use the Repo.get/3 function to fetch a record from the database given its ID.

Ecto queries are used to retrieve data from a repository. More on queries later. We can also fetch records that meet a given criteria with the Repo.get_by/3 function. This function requires two arguments: the “queryable” data structure and the clause with which we want to query.

There are two primary APIs: cast_assoc/3 and cast_embed/3 – those functions are used when working with external data. In particular, they allow you to change associations and embeds alongside the parent struct, all at once. put_assoc/4 and put_embed/4 – it allows you to replace the association or embed as a whole.

Due to the prevalence of the pipe operator in Elixir, Ecto also supports a pipe-based syntax: The keyword-based and pipe-based examples are equivalent. The downside of using macros is that the binding must be specified for every operation.

In the query below u is a binding and u.age is a field access using this binding. Bindings are not exposed from the query. When composing queries, you must specify bindings again for each refinement query. For example, to further narrow down the above query, we again need to tell Ecto what bindings to expect:

Any value can be used on the right-hand side of in as long as it implements the Ecto.Queryable protocol. For now, we know the protocol is implemented for both atoms (like User) and strings (like “users”). In any case, regardless if a schema has been given or not, Ecto queries are always composable thanks to its binding system.

On the left-hand side of in we specify the query bindings. This is done inside from and join clauses. In the query below u is a binding and u.age is a field access using this binding. Bindings are not exposed from the query.