Ecto

Handles external data such as databases and JSON APIs

• Repo
• Query
• Schema
• Changset

Repo: communicates with external data source or database #

Has common methods:

• get(): gets the record
• insert(): creates the record in that database
• update()
• delete()
• transaction() …

Phoenix uses Repo through:

• config.exs as config :appname, Appname.Repo, …
• repo.ex in /lib/appname/repo.ex

Common methods #

Repo.count()
Repo.update_all("tablename", set: [updated_at: Ecto.DateTime.utc])

Schema #

Reusable data-model for moving data around. Schemas are a useful shortcut used in querying so you don’t have to specify all the attributes

Schema Associations #

sets relationships between tables

• has_many
• has_one
• belongs_to
• many_to_many

Virtual Attributes #

Disposable attributes that are not saved to the database. For example, an office address that is used to get a latitude and longitude to store in the database, without storing the office address

Embedded Schema #

A schema that doesn’t use a datbase

Changeset #

Allows manipulation of the data to match Schema so that it can be passed to the Repo

• Cast: filters the parameters with the attributes to be accepted into the changeset
• Validate: validates those filtered attributes. This includes constraints which are set on the database level

Defining #

def changeset(schemaname, attrs) do
  schemaname
  |> cast(attrs, [:key1, :key2,..])
  |> validate_required([:key1])
  |> validate_inclusion(:name, ["John", "Jack"])
  |> validate_exclusion(:name, ["Jub Jub"])
  |> validate_length(:country, is: 2)
  |> validate_length(:password, min: 8, max: 32)
end

Calling #

attrib_name = get_field(changeset, :attrib_name)

Schemaless Changeset #

Defining #

model = %{key1: :string, key2: string} 
attributes = %{key1: "value", key2: "value"}    
changeset = {%{}, model}
  |> cast(attributes, Map.keys(model))
  |> validate_required([:key1])
end

Ecto Queries (see other article) #

Phoenix #

Phoenix Ecto #

allows changeset shortcuts into forms