Csv Schema

Csv schema is a library helping you to build Ecto.Schema-like modules having a csv file as source.

The idea behind this library is give the possibility to create, at compile-time, a self-contained module exposing functions to retrieve data starting from a CSV.

Installation

If available in Hex, the package can be installed by adding csv_schema to your list of dependencies in mix.exs:

def deps do
  [
    {:csv_schema, "~> 0.2.0"}
  ]
end

Usage

Supposing you have a CSV file looking like this:

Is possible to create an Ecto.Schema-like repository using Csv.Schema macro:

defmodule Person do
  use Csv.Schema
  alias Csv.Schema.Parser

  schema "path/to/person.csv" do
    field :id, "id"
    field :first_name, "first_name", filter_by: true
    field :last_name, "last_name", sort: :asc
    field :identifier, ["first_name", "last_name"], key: true, join: " "
    field :email, "email", unique: true
    field :gender, "gender", filter_by: true, sort: :desc
    field :ip_address, "ip_address"
    field :date_of_birth, "date_of_birth", parser: &Parser.date!(&1, "{0M}/{0D}/{0YYYY}")
  end
end

Note that it's not a requirement to map all fields, but every field mapped must have a column in csv file. For example the following field configuration will result in a compilation error:

field :id, "non_existing_id", ....

Schema could be configured using a custom separator

use Csv.Schema, separator: ?,

Moreover it's possible to configure if csv file has or has not an header. Depending on header param value field config changes:

# Csv with header
schema "path/to/person.csv" do
  field :id, "id", key: true
  ...
end

# Csv without header. Note that field 1 is binded with the first csv column.
# Index goes from 1 to N
schema "path/to/person.csv" do
  field :id, 1, key: true
  ...
end

Now Person module is a struct, defined like this:

defmodule Person do
  defstruct id: nil,
            first_name: nil,
            last_name: nil,
            email: nil,
            gender: nil,
            ip_address: nil,
            date_of_birth: nil
end

This macro creates for you inside Person module those functions:

def by_id(integer_key), do: ...

def filter_by_first_name(string_value), do: ...

def by_email(string_value), do: ...

def filter_by_gender(string_value), do: ...

def get_all, do: ...

Where:

• by_id returns a %Person{} or nil if key is not mapped in csv
• filter_by_first_name returns a [%Person{}, %Person{}, ...] or [] if input predicate does not match any person
• by_email returns a %Person{} or nil if no person have provided email in csv
• filter_by_gender returns a [%Person{}, %Person{}, ...] or [] if input predicate does not match any person gender
• get_all return all csv rows as a Stream

Field configuration

Every field should be formed like this:

field {struct_field}, {csv_header}, {opts}

where:

• {struct_field} will be the struct field name. Could be configured as string or as atom
• {csv_header} is the csv column name from where get values. Must be configured using string only
• {opts} is a keyword list containing special configurations

opts:

• :key : boolean. At most one key could be set. If set to true creates the by_{name} function for you.
• :unique : boolean. If set to true creates the by_{name} function for you. All csv values must be unique or an exception is raised
• :filter_by : boolean. If set to true creates the filter_by_{name} function
• :parser : function. An arity 1 function used to map values from string to a custom type
• :sort : :asc or :desc. It sorts according to Erlang's term ordering with nil exception (number < atom < reference < fun < port < pid < tuple < list < bit-string < nil)
• :join : string. If present it joins the given fields into a binary using the separator

Note that every configuration is optional

Keep in mind

Compilation time increase in an exponential manner if csv contains lots of lines and you configure multiple fields candidate for method creation (flags key, unique and/or filter_by set to true).

Because "without data you're just another person with an opinion" here some data:

5 compilations average time.

Executed on my machine:

Lenovo Thinkpad T480
CPU: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
RAM: 32GB