问题
Whats the quickest way to see the number of entries in my database? I'd like to see the number of posts in my posts/index view.
Say I have a Post model and a bunch of posts saved in my database. In Rails I could do something like this in a view file:
<h1><%= @posts.length %> Posts</h1>
or
<h1><%= @posts.size %> Posts</h1>
or
<h1><%= @posts.count %> Posts</h1>
What's the Phoenix Framework/Elixir equivalent?
回答1:
If you've already loaded the posts in memory in your controller using Repo.all, you can use length/1 to count the number of items in the list. This is equivalent to .length in Ruby/Rails.
length(@posts)
If you want to run the count query in the database instead, you can do:
Repo.one(from p in Post, select: count("*"))
You can also add where: filter to the query to restrict the posts to e.g. created by a specific user. This is equivalent to doing .count in Rails.
回答2:
The options that Dogbert has provided are both correct and should be used for Ecto 1.x.
In Ecto 2.0 you can use Repo.aggregate/4
Repo.aggregate(Post, :count, :id)
来源：https://stackoverflow.com/questions/36683238/count-the-number-of-entries-in-an-ecto-repository