pquery

    0.3.4 • Public • Published

    PQ: Human Readable Promise Chain Query Compiler

    Promises are awesome. But when it comes to write promise chains, it becomes kind of hard to write. PQ solves this issue and allows you to create human readable promise chains

    npm version Build Status

    • Make your Promises more human-readable.
    • Allows to create your own DSL.
    • Zero-dependency.

    Debug

    pq.debug() gives you a cool debugger to debug your queries

    Install

    You can simply use NPM/Bower to download pq.

    # Using NPM
    npm install pquery --save
    
    # Using Bower
    bower install pquery --save
    

    Overview

    What you write:

    pq("(name, surname) of users of @json of #fetch('/users')").then(...)
     
    // or more functional
    pq(fetch("/users"), "(name, surname) of users of @json").then(...)
     
    // or Unix way
    pq("#fetch('/users') | @json | users | (name, surname)").then(...)
     
    // or reverse pipeline
    pq("(name, surname) <| users <| @json <| #fetch('/users')").then(...)

    This is actually what you run:

    fetch("/users").
      then(function (response) {
        return response.json()
      }).
      then(function (response) {
        return response.users
      }).
      then(function (response) {
        return response.map(function (object) { return {
          name: object.name,
          surname: object.surname
      }})
    })

    Why?

    I use promises in many cases in my daily work. And calling a promise chain is a bit boring to write. I used to write then keyword again and again to create a chain and this drive me crazy, they seem ugly.

    So, I created pq to make this chains easier to write and easier to read.

    Let's checkout a real-world promise example:

    var foo = fetch("/hello")
     
    foo.then(function (response) {
      return response.json()
    }).then(function (response) {
      return response.data
    }) // this then's may go to the sky, or the hell!

    This is how to write this using pq:

    pq(foo, "data of @json")

    Queries are Powerful Strings

    Since pq is just a string, you can create queries anywhere you want and these may be handy to write your own DSL. Here is a real-world example:

    Instead of writing this promise chain:

    fastfood().
    then(function (response) {
      return response.menus
    }).
    then(function (response) {
      return response.find({name: 'hamburger'})
    }).
    then(function (response) {
      return response.items()
    }).
    then(function (response) {
      return response.map(function (res) {
        return {
          name: res.name,
          price: res.price
        }
      })
    }).
    then(function (response) {
      $("ul").append($("<li/>").html(`${response.name} ${response.price}`))
    })

    Just write this:

    <ul data-pq="(name, price) of @items of find({name: 'hamburger'}) of menus">
      {% $data.forEach(function (item) { %}
      <li> {{ item.name }} costs {{ item.price }} </li>
      {% }) %}
    </ul>

    How to Write Queries

    There are few simple rules to write a readable query:

    Promise Chain Keywords

    then and of are main keywords to generate promise chains. foo then bar is actually foo.then(function (r) { return r.bar }). Since they are chained, the left part of chain must have the right of the chain.

    of (reverse promise keyword) makes the query more readable. Just like the SQL, you define what you want at first. bar of foo is foo.then(function (r) { return r.bar }), too.

    Keyword Description Example
    .. then or .. -> .. or |> or | Simple promise chain @json then data, @json -> data
    .. of .. or .. <- .. or <| Simple promise chain, reversed data of @json, data <- @json

    You can use of and then together: full_name of user then last_letter of first_name. This will be run like: (full_name of user) then (last_letter of first_name), which is actually user then full_name then first_name then last_letter.

    If it becomes confusing to you, do not use them together

    Meta Characters (Optional)

    Meta characters are optional. But they want to make your query easier to read/write. If you want to call a function, you can just put a @ character beginning of it. @json will be converted to json().

    The most useful meta character is %{number}. It allows you to pass arguments to the pq. ("a of %1", "b") will be a of b.

    Character Description Example Equivalent
    @ Method Calling @methodName methodName()
    %{number} Simple Parameters pq(promise, "%1 of @json", "hello") pq(promise, "hello of @json")
    & This Object &.length of users of @json this.length of users of json()
    # Single Call @json of #fetch(...)
    ! Promisify response of !functionWithCallback

    Tutorial

    This is a simple, delayed Promised function:

    function sauces(id) {
      return function () {
        return new Promise(function (resolve) {
          return resolve({
            items: id == 1 ? [
              {name: "Ketchup"},
              {name: "Mustard"}
            ] : [
              {name: "BBQ"},
              {name: "Mayonnaise"}
            ]
          })
        })
      }
    }
     
    function burgers() {
      return new Promise(function (resolve) {
        setTimeout(function () {
          return resolve({
            items: [
              {name: "McChicken", price: "$10", sauces: sauces(1)},
              {name: "Big Mac", price: "$15", sauces: sauces(2)},
            ]
          })
        }, 1000)
      })
    }

    Let's query this using pq:

    pq(burgers(), "(price) of items").then(function (prices) {
      console.log(prices) // [{price: "$10", price: "$15"}]
    })

    Let's make it more complex:

    pq(burgers(), "(name) of items of @sauces of items[0]").then(function (sauce) {
      console.log(sauce) // [{name: "Ketchup"}, {name: "Mustard"}]
    })

    How to Write Custom Parsers

    It's too easy to add custom parsers using pq.parse command:

    pq.parse(function (query) {
      return query.replace(/^gh\:([^\s]+)/, "#fetch('https://api.github.com/$1?page=1&per_page=100')")
    })
     
    pq.parse(function (query) {
      return query.replace(/([^\s]+)\s*~=\s*([^\s]+)/, "filter(function (n) {return n.$1 == '$2'})")
    })

    Then you'll be able to use your custom parsers.

    pq("name~=delorean of @json of gh:users/f/repos").then(function (result) {
      console.log(result)
    })

    Query Reducers

    Query reducers helps you to manage your data flow easier.

    pq.before

    pq.before will give you the raw query so you can make changes on it on-the-fly.

    pq.before(function (query) {
      // You can change query before compilation
      return query
    })

    pq.after

    pq.after will give you compiled promise fragments.

    pq.after(function (queries) {
      // You can change queries after it's compiled
      return queries.push(pq.compile_fragment("@json"))
    })

    License

    MIT Licensed - Copyright © 2016 by Fatih Kadir Akın

    Keywords

    Install

    npm i pquery

    DownloadsWeekly Downloads

    27

    Version

    0.3.4

    License

    MIT

    Last publish

    Collaborators

    • fkadev