The latest version of Elixir introduced many functionalities that can be very useful for a developer. One of the most significant changes is the new macro that allows for better debugging your code behavior.
This post is a quick analysis of the possibilities offered by dbg/2.
Kernel.dbg/2
Macro allows us to analyze our code. Let’s look at the following usage example:
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def otp_already_sent?(email) do
min_valid_datetime = DateTime.utc_now() |> Timex.shift(minutes: -@code_ttl_in_minutes)
from(q in LoginOTP,
where: q.email == ^email,
where: q.generated_at >= ^min_valid_datetime,
limit: 1
)
|> Repo.one()
|> case do
nil -> false
%LoginOTP{} -> true
end
|> dbg() # <----- NEW CODE HERE
end
Putting the dbg/2 call at the end, we can get information about the execution of our software:
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# File location
[(core 0.1.0) lib/core/otp_generator.ex:42: Core.OTPGenerator.otp_already_sent?/1]
# First line
from(q in LoginOTP,
where: q.email == ^email,
where: q.generated_at >= ^min_valid_datetime,
limit: 1
) #=> #Ecto.Query<from l0 in Core.LoginOTP,
where: l0.email == ^"test@example.com",
where: l0.generated_at >= ^~U[2022-09-26 11:39:00.794321Z], limit: 1>
# Second line
|> Repo.one() #=> %Core.LoginOTP{
__meta__: #Ecto.Schema.Metadata<:loaded, "login_otps">,
id: "7375c128-0703-41ea-96b5-4d0af850094a",
email: "test@example.com",
code: "229436",
generated_at: ~U[2022-09-26 11:54:00Z]
}
# Third line
|> case do
nil -> false
%LoginOTP{} -> true
end #=> true
For the sake of clarity of the example above, I have introduced additional separations and indicated which line the result applies to.
As you can see, after # =>, we get the current binding with which the command was executed.
By itself, dbg/2 returns the value of the debugged code, which can be extremely useful.
Change in debugging
The introduced code testing capabilities may facilitate the work.
Instead of entering |> IO.inspect(label: "Some step") after each line, and you need to specify |> dbg() in one place, especially at the end of our pipeline.
You can customize the dbg/2 function to suit your needs.
For this purpose, you can use the functionality described in the documentation: Configuring the debug function.