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Writing Queries with Schemas

Programming Ecto — Pragmatic Programmers (30 / 122)

👈 Creating Schemas | TOC | Inserting and Deleting with Schemas 👉

When we looked at queries in the last chapter, we deliberately chose to write them without schemas. This is still a good choice in some circumstances, but schemas provide some helpful shortcuts and we promised that we’d revisit them later. Now’s the time. In this section, we’ll start writing queries that work with schemas, and we’ll also consider when it’s best not to.

Let’s look at a query we ran in the last chapter:

In addition, we have to use the select option to specify what columns we want returned to us. This is not so bad since we’re only fetching one value, but consider what this would look like with the tracks table:

Specifying all those fields every time could get tedious quickly.

Schemas can help us with both of these issues. Using our new %Track{} schema, we can rewrite the query like this:

Notice that we’ve replaced the string “tracks” with the name of the schema module we created earlier. This tells Ecto that our query is referencing a schema, rather than the name of a database table. Adding the alias in the first line lets us use the module name without its full namespace — most Ecto developers follow this convention.

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