Counting Records With Ecto

Sometimes you want to know how many records there are in a table. Ecto gives us a couple ways to approach this.

We can use the count\1 function that the Ecto query API provides.

> Repo.one(from p in "people", select: count(p.id))

16:09:52.759 [debug] QUERY OK source="people" db=1.6ms
SELECT count(p0."id") FROM "people" AS p0 []
168

Alternatively, we can use the fragment/1 function to use PostgreSQL's count function.

> Repo.one(from p in "people", select: fragment("count(*)"))

16:11:19.818 [debug] QUERY OK source="people" db=1.5ms
SELECT count(*) FROM "people" AS p0 []
168

Lastly, Ecto.Repo has the aggregate/4 function which provides a :count option.

> Repo.aggregate(from(p in "people"), :count, :id)

16:11:23.786 [debug] QUERY OK source="people" db=1.7ms
SELECT count(p0."id") FROM "people" AS p0 []
168