jql

Hey there!

You're probably here cause you're fed up with other json query processors being too complicated to use for anything surpassing simple single field selection.

Well, at least that's what led me here. And that's why I've written jql, a json query processor with an even more cryptic - lispy - syntax (Maybe not that cryptic after all? I quite like it :) )

jql aims to be friendly, helpful, pat you on the back when you're faced with a monstrosity of a JSON blob. Help you mold it into something useful, step by step.

If you want to see benchmarks, they're at the end of the README.

If you want to see a cheatsheet with function types, it's right before the benchmarks.

Ok, let's check it out now, but first things first, you have to install it:

go install github.com/cube2222/jql

Ok. Done.

If you don't have the Go toolchain installed, just download one of the release binaries.

If you want an interactive window to get live output for queries, use:

echo '' | fzf --print-query --preview-window wrap --preview 'cat test.json | jql {q}'

Let's check out a few simple examples. (remember? That's explicitly not why we're here. But it aids understanding of the more complex examples, so stay with me just a little bit longer!)

We'll be working with this piece of json:

{ 
  "count": 3,
  "countries": [
    {
      "name": "Poland",
      "population": 38000000,
      "european": true,
      "eu_since": "2004"
    },
    {
      "name": "United States",
      "population": 327000000,
      "european": false
    },
    {
      "name": "Germany",
      "population": 83000000,
      "european": true,
      "eu_since": "1993"
    }
  ]
}

To start with, let's get the countries array only.

> cat test.json | jql '(elem "countries")'
[
  {
    "eu_since": "2004",
    "european": true,
    "name": "Poland",
    "population": 38000000
  },
  {
    "european": false,
    "name": "United States",
    "population": 327000000
  },
  {
    "eu_since": "1993",
    "european": true,
    "name": "Germany",
    "population": 83000000
  }
]

Whoa, whoa, whoa! What's up with the parentheses?!

Remember what I said before? Lispy syntax. In short, whenever you see (add 1 2), it's basically the same as add(1, 2). I like that syntax for big hierarchical expressions, if you really really really don't like it, then you can probably stop right here, though you'll be losing out!

I've warned you.

What if we wanted only the first country from that list?

> cat test.json | jql '(elem "countries" (elem 0))'
{
  "eu_since": "2004",
  "european": true,
  "name": "Poland",
  "population": 38000000
}

Let's break down what happened here. First we took the "countries" field. elem takes an additional argument, it says "how to transform the element" and is also an expression. Here we say we want to take the first element of the countries array. The default function is id, which stands for identity.

array

We can also pass an array of positions to elem, to get more than one country:

> cat test.json | jql '(elem "countries" (elem (array 0 2)))'
[
  {
    "eu_since": "2004",
    "european": true,
    "name": "Poland",
    "population": 38000000
  },
  {
    "eu_since": "1993",
    "european": true,
    "name": "Germany",
    "population": 83000000
  }
]

elem can work with single strings, single integers, arrays of those, and objects with them as values (but we won't cover those now to keep things simple).

keys

What if we want to get all the country names? A new friend - keys - is key in this situation. 🗝

cat test.json | jql '(elem "countries" (elem (keys) (elem "name")))'
[
  "Poland",
  "United States",
  "Germany"
]

It returns an array of all the keys of the given collection. Fields and Indices for Objects and Arrays respectively.

To illustrate, here's keys used on an object:

> cat test.json | jql '(elem "countries" (elem 0 (keys)))'
[
  "name",
  "population",
  "european",
  "eu_since"
]

Attention

Now we have to understand a very important mechanism underlying jql. All functions operate in the context of the JSON we're operating on.

Some functions, like elem, will cut down the context for expressions it evaluates. The first argument - which should evaluate to the positions we need - gets evaluated in the context of the entire array, that's why keys returns all the indices. The second one on the other hand, operates in the context of a single element.

In theory we're really just creating and composing a big function - pipeline, so to say - which gets applied to our JSON blob.

This may sound complicated, but I find it becomes intuitive quite quickly.

You can see that elem is the most used function, and in fact it's what you'll usually be using when munging data, so there's a shortcut. If you put a value in function name position, it implicitly converts it to an elem.

This way we can rewrite the previous query to be much shorter, and better match the shape of the data.

> cat test.json | jql '("countries" ((keys) ("name")))'
[
  "Poland",
  "United States",
  "Germany"
]

Little showcase

Remember when I said you can use integers, strings, arrays and objects as positions?

> cat test.json | jql '("countries" ((array (array 0 (array 0 (array 0 (array 0 2)))) 1 (object "key1" 1 "key2" (array 0 (object "key1" 1 "key2" (array 0 2))))) ("population")))'
[
  [
    38000000,
    [
      38000000,
      [
        38000000,
        [
          38000000,
          83000000
        ]
      ]
    ]
  ],
  327000000,
  {
    "key1": 327000000,
    "key2": [
      38000000,
      {
        "key1": 327000000,
        "key2": [
          38000000,
          83000000
        ]
      }
    ]
  }
]

🔥🔥🔥

Don't do this.

range

We can also select a range of elements, using the... you guessed it - range function.

> cat test.json | jql '("countries" ((range 1 3) ("name")))'
[
  "United States",
  "Germany"
]

You can use the array function in value position too obviously. If you want a list of name-population tuples you can just

> cat test.json | jql '("countries" ((keys) (array ("name") ("population"))))'
[
  [
    "Poland",
    38000000
  ],
  [
    "United States",
    327000000
  ],
  [
    "Germany",
    83000000
  ]
]

Here you can see that array passes the whole context given to it to each of its arguments. (Reminder: We're using "name" and "population" as elem shortcuts here.)

Most functions work like this. Only elem is the "context-cutdowner", so to say.

object

You can also use object to create objects, with arguments alternating keys and values.

> cat test.json | jql '(object
                            "names" ("countries" ((keys) ("name")))
                            "populations" ("countries" ((array 0 0 1) ("population"))))'
{
  "names": [
    "Poland",
    "United States",
    "Germany"
  ],
  "populations": [
    38000000,
    38000000,
    327000000
  ]
}

zip

Occasionally you might want to combine multiple arrays, you can use zip to do that. For example, to create a list of key-value entries from an object, you can do the following:

> cat test.json | jql '("countries" 
                           (0 (zip 
                                 (keys) 
                                 ((keys)))))'
[
  [
     "eu_since",
     "2004"
  ],
  [
     "european",
     true
  ],
  [
     "name",
     "Poland"
  ],
  [
     "population",
     38000000
  ]
]

Now we're done with the core functionality of jql. The stuff so far will probably suffice for most use cases and even very complex data structures.

However, here come more functions:

String manipulation 🎻

join

If you ever need to join an array of expressions into a string, join's the mate you're looking for! join will also stringify anything it meets. Without separator:

> cat test.json | jql '("countries" ((keys) (join (array ("name") ("population") ("european")))))'
[
  "Poland3.8e+07true",
  "United States3.27e+08false",
  "Germany8.3e+07true"
]

With separator:

> cat test.json | jql '("countries" ((keys) (join (array ("name") ("population") ("european")) ", ")))'
[
  "Poland, 3.8e+07, true",
  "United States, 3.27e+08, false",
  "Germany, 8.3e+07, true"
]

sprintf

Whenever I learn a new language, I feel much more comfortable when I know there's a sprintf function. (and how to use it)

Anyways, here you go, the syntax is the same as that of the go standard library fmt.Sprintf function:

> cat test.json | jql '("countries" ((keys) (sprintf "%s population: %.0f" ("name") ("population"))))'
[
  "Poland population: 38000000",
  "United States population: 327000000",
  "Germany population: 83000000"
]

Hope you're feeling comfortable 🛋 now :)

error

There's a little helper function - error - for those times when you're debugging your queries.

It's an expression which errors on evaluation and gives you a stack trace. It can also evaluate and print any expression you want in it's context.

> cat test.json | jql '("countries" ((keys) (sprintf "%s population: %.0f" ("name") (error "test message"))))'
2019/12/26 00:17:04 error getting expression value for object: couldn't get transformed value for field countries with value [map[eu_since:2004 european:true name:Poland population:3.8e+07] map[european:false name:United States population:3.27e+08] map[eu_since:1993 european:true name:Germany population:8.3e+07]]: couldn't get element using position at array index 0: couldn't get transformed value for index 0 with value map[eu_since:2004 european:true name:Poland population:3.8e+07]: couldn't evaluate sprintf argument with index 1: Message: test message
goroutine 1 [running]:
runtime/debug.Stack(0xc0000723f0, 0x1114e00, 0xc0000744e0)
        /usr/local/Cellar/go/1.13.4/libexec/sr

Jql

Install / Use

README

jql