Programming Ecto (Pragprog)

You can look at hexpm the application that runs Examples of context modules using multis are: Keys, Users, and Releases.


I have started reading the book and got problem with fist exercise. I think the code provided with the book though pragrpog website is incomplete:

    08:54:23.966 [debug] QUERY OK db=2.4ms
INSERT INTO "genres" ("name","wiki_tag","inserted_at","updated_at") VALUES ($1,$2,$3,$4) RETURNING "id" ["jazz", "Jazz", {{2018, 8, 22}, {22, 54, 23, 958894}}, {{2018, 8, 22}, {22, 54, 23, 958900}}]

08:54:23.970 [debug] QUERY OK db=4.0ms
commit []

08:54:23.971 [debug] QUERY OK db=0.4ms queue=0.1ms
begin []

08:54:23.973 [debug] QUERY OK db=2.4ms
INSERT INTO "genres" ("name","wiki_tag","inserted_at","updated_at") VALUES ($1,$2,$3,$4) RETURNING "id" ["live", "Concert", {{2018, 8, 22}, {22, 54, 23, 971190}}, {{2018, 8, 22}, {22, 54, 23, 971196}}]

08:54:23.974 [debug] QUERY OK db=0.4ms
commit []
** (UndefinedFunctionError) function MusicDB.Note.__schema__/1 is undefined (module MusicDB.Note is not available)
    (ecto) lib/ecto/changeset/relation.ex:138: Ecto.Changeset.Relation.change/3
    (ecto) lib/ecto/repo/schema.ex:597: anonymous fn/4 in Ecto.Repo.Schema.surface_changes/3
    (elixir) lib/enum.ex:1925: Enum."-reduce/3-lists^foldl/2-0-"/3
    (ecto) lib/ecto/repo/schema.ex:584: Ecto.Repo.Schema.surface_changes/3
    (ecto) lib/ecto/repo/schema.ex:189: Ecto.Repo.Schema.do_insert/4
    (ecto) lib/ecto/repo/schema.ex:125: Ecto.Repo.Schema.insert!/4
    priv/repo/seeds.exs:15: (file) 

I have check the code and function MusicDB.Note is missing.

Hi @sergek. Sorry for the trouble - I screwed up the source code when we pushed the last beta, and didn’t catch this. :disappointed:

I’ve submitted a fix, so if you download the latest version of the source from the book’s webpage, everything should be working again.

Please give that a try, and post again if you’re still having trouble. Thanks for your patience! :heart:


Thank you for the prompt fix! :grinning:

It did work much better this time. Although this time I got warnings like the ones below:
==> music_db
Compiling 14 files (.ex)
warning: invalid association notes in schema MusicDB.Artist: associated schema MusicDB.Note does not have field artist_id
lib/music_db/artist.ex:9: MusicDB.Artist (module)

warning: invalid association `notes` in schema MusicDB.Track: associated schema MusicDB.Note does not have field `track_id`
  lib/music_db/track.ex:9: MusicDB.Track (module)

warning: invalid association `notes` in schema MusicDB.Album: associated schema MusicDB.Note does not have field `album_id`
  lib/music_db/album.ex:9: MusicDB.Album (module)

Is that something to worry about?


It shouldn’t block you from working with the code, and we’ll get rid of the warning in the next beta :slightly_smiling_face:

1 Like

Thanks Darin,

So far so good! Book is awesome - I am very glad I bought it.


1 Like



Does anyone know whether this book will be updated to reflect the changes in Ecto 3.0?

Thanks in advance!

Posted on July 1st above :slight_smile: .



1 Like


This is just to let you know that Programming Ecto (eBook) has recently been updated. You own an electronic version of this book, and so you’ll be able to download this latest version.

Changes in This Release

  • Added chapter 17, Tuning For Performance
  • Made several edits and additions throughout to book to reflect the changes for Ecto 3.0
  • Fixed many errata

Aaaaand that’s a wrap - the book is officially completed and released!

Thanks to all who participated in the beta - the early feedback was super helpful :heart:


Interim-review (continued in post below)

It’s summer here and as I try not being glued to my desk all day, I needed a book to read where it wasn’t strictly necessary to follow along with the examples. I chose this book after what @peerreynders said in his post above :smiley:

I’m only 60% of the way through this book (chapters 1-6 as per Peer’s recommendation, and will be going back to Programming Phoenix now - edit - I actually ended up finishing the book as I was enjoying it so much! See the rest of my review in the post below…) but I just wanted to post a mini-review to say I’m really really really loving this book! It’s been one of the most enjoyable Elixir books I’ve read so far. Why? Because it’s sooooooooooooooooooooooooooooo easy to read!! :lol:

There are a number of reasons for this, in part it is because of the pace and well thought out progression of topics, but the thing I really appreciated, is that it seems to have been produced with those of us who use e-readers in mind; there’s absolutely no having to flick back through pages to review code that is spoken about. Code is either just before or just after it’s covered or (and I really appreciate this…) repeated if it is spoken about again. The output is also included, eradicating the need to actually follow along as the results are there in front of you. On top of that, since everything is well explained and at an even pace, the cognitive load required to progress through the book is relatively low if you already know the basics of SQL. All this makes reading on e-readers frustration free and a real joy.

The other thing I really like about this book is that it acts as a bit of a SQL refresher (in fact so far my only suggestion would have been to run with this and cover more SQL and how to do it with Ecto - though I’m guessing the remainder of the book may do some of that anyway).

The other reason I like this book is because it (perhaps obviously) showcases what’s so great about Ecto. Ecto has been put together very nicely and I like that it follows the Elixir theme of keeping magic to a minimum. The query syntax is pretty close to SQL query syntax, and I think this will make converting SQL to Ecto a lot easier than trying to do the same in other DB libraries or ORMs such as Active Record. It will also mean if you ever need to drop into raw SQL it should be a bit easier.

So my thoughts so far are… get this book!! It’s so incredibly easy to read that I’m pretty sure you’ll enjoy it just as much as I am!

Well done Eric and Darin! :023:


My review - continued…

I’ve now finished this book! So here’s the rest of my review :003:

I’ll start by saying that I wasn’t really sure what I was expecting from this book - I mean, how deep can a database library be? Or how involved might it be using one? Of course that was based on my experience with ActiveRecord. Well it turns out a DB library can be more than what you may be used to or expect, and I was very pleasantly surprised by this book as well as Ecto itself.

One of the things I’ve said numerous times about Elixir - that it and the community show us a ‘better way’ - is most definitely echoed in this book! Some of the things I learned that I didn’t know before are that I can create custom Ecto types, or use table-less schemas, or that polymorphism can be handled in several different ways - all with different pros and cons.

I also learned about upserts and transactions and as I mentioned in the book club thread, there was a very welcomed chapter on application design which covers separating the Pure from the Impure, (Phoenix) Contexts and Umbrellas! I really wasn’t expecting to see that in a book about Ecto and it was definitely very much appreciated.

I also enjoyed the chapter and details regarding Phoenix, and I agree with @peerreynders that it may actually be beneficial to read this book before Programming Phoenix (or as I did, after the initial part of it) - it is so easy to read and doesn’t require much cognitive load if you are already familiar with the basics of SQL and something like ActiveRecord, so you will finish it in no time!

Miss this book at your peril! It will show you why Ecto is different… and why Ecto guides you down a ‘better’ path. Isn’t that in part why we came to Elixir?

Well done @darinwilson and @ericmj (and for all your work on Ecto!) :023:


Nice review; now I’m even more excited to dig into this book after I revisit Programming Elixir >= 1.6 and work through Elixir in Action. :tada:

Thanks for reiterating this point; I’m going to follow suit. :spades: :diamonds: :clubs: :purple_heart:


Nice one @Ted! Let us know how you get on :003:

You have selected great books so you can’t go wrong no matter which order you may end up reading them :023:

I started a related thread here so as to not go off-topic in this thread :smiley:

I started reading the book and I agree with @AstonJ the book is very easy to follow :point_up: (I am far from being a DB expert) knowing how important Ecto in the elixir ecosystem reading it is a no brainer for anyone learning elixir or phoenix

This is my favorite elixir book so far :heart:

Thank you to the authors @darinwilson @ericmj and to everyone involved in this project!


This is my next book.


Just wanted to stated that I enjoyed this book a lot. :grinning:
Thank you @ericmj and @darinwilson for putting this together.

Favourite aspects of the book.

• I liked that Part I - Ecto Fundamentals encourages the reader to test and play with all the key features of Ecto. It made the book easy to jump into and kept me focused on first playing and testing things out. The ability to “play” is a key feature for learning.

• A lot of knowledge about Querying, Changesets, Schemas before even dealing with migrations. Thinking about structure, tables, columns and table joins later on in the book was a good move.

• Appreciate the ability to always reset the test data in the demo app.

Part II - Optimizing IEx for Ecto. I had no clue you can do that. Huge time saving tip for customizing IEx.

• Embedded schemas. Did not realize some of the things you can do with embedded schemas.

• Performing upserts with :on_conflict chapter. This now makes a lot of sense.

Whether your a beginner or an expert in Elixir this book is easy and fun to go through. I have already started refactoring some code on a current project with the new knowledge I have on Ecto.

Highly recommend the book. :+1:


Thanks for the nice feedback @neuone - I’m glad you found the book helpful!

1 Like