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, "~> 0.1.0"}
  ]
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", key: true
    field :first_name, "first_name", filter_by: true
    field :last_name, "last_name"
    field :email, "email", unique: true
    field :gender, "gender", filter_by: true
    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", ....

Moreover it's possible to pass to use Csv.Schema the :separator param. This let the macro split csv for you using provided separator.

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

Note: if @auto_primary_key is set to true this macro creates automatically a new column called id (and new by_id method). Its value is a progressive integer; otherwise you have to set a key opt to the field that should be key

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

Note that every configuration is optional

Keep in mind

Compilation time increase in a linear 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