Constraints are only tested after you do a repository operation, such as Repo.insert, since it is the database reporting what is wrong (rather than we testing it).
josevalim
Creator of Elixir
kostonstyle
josevalim
Creator of Elixir
Yes, that’s by definition how constraints in Ecto work. They rely on the
database as the da abase is the only one who can effectively say if that
relationship exists or not.
2
kostonstyle
My last question(hopefully 
), when I tried to insert into db, I’ve got an exception:
iex(5)> e = Repo.insert(c)
[debug] QUERY ERROR db=16.0ms
INSERT INTO "countries" ("iso_country","iso_language","name","inserted_at","updated_at") VALUES ($1,$2,$3,$4,$5) RETURNING "id" ["YY", "DE", "Schweiz", {{2016, 11, 24}, {13, 28, 8, 0}}, {{2016, 11, 24}, {13, 28, 8, 0}}]
** (Ecto.ConstraintError) constraint error when attempting to insert struct:
If you would like to convert this constraint into an error, please
call foreign_key_constraint/3 in your changeset and define the proper
constraint name. The changeset defined the following constraints:
How to get a message instead raised exception?
In doc Ecto.Repo — Ecto v3.14.0 it says, I should get a tuple.
Thanks
0
josevalim
Creator of Elixir
Can you post the full message? The error message is telling exactly what you need to do. You need to pass the :name option to foreign_key_constraint/3 with the foreign key name that is failing.
0
kostonstyle
I’ve found the solution:
def changeset(struct, params \\ %{}) do
struct
|> cast(params, [:iso_country, :iso_language, :name])
|> validate_required([:iso_country, :iso_language, :name])
|> foreign_key_constraint(:iso_country)
|> foreign_key_constraint(:iso_language)
end
It works as expected.
At last, what is the :name options for, that I can pass?
0
kostonstyle
kostonstyle
So I will post the final code, that works.
schema "countries" do
field :iso_country, :string
field :iso_language, :string
field :name, :string
timestamps
end
def changeset(struct, params \\ %{}) do
struct
|> cast(params, [:iso_country, :iso_language, :name])
|> validate_required([:iso_country, :iso_language, :name])
|> foreign_key_constraint(:iso_country)
|> foreign_key_constraint(:iso_language)
end
Look at the function foreign_key_constraint, I do not pass the name option parameter and it works. Why? What is the use of the name option parameter?
0
josevalim
Creator of Elixir
The name option would be given to the foreign_key_constraint function. If it works without passing the :name option, it means Ecto is guessing the proper name for you.
0
kostonstyle
So, when I what to pass the :name option, how do I have to write?
The migration of countries looks as follow:
create table(:countries) do
add :iso_country, references(:countries_code, column: :iso, type: :string)
add :iso_language, references(:languages_code, column: :iso, type: :string)
add :name, :string
timestamps
end
Thanks
0