# PQL Language Features
PQL adds several language features over GQL. This is a summary of them.
# Operators
Standard operations, such as not, or, and, if, equals, isNull, sprintf and many others, are supported as fields:
1. ?query=not(true)
2. ?query=or([1,0])
3. ?query=and([1,0])
4. ?query=if(true, Show this text, Hide this text)
5. ?query=equals(first text, second text)
6. ?query=isNull(),isNull(something)
7. ?query=sprintf(%s API is %s, [PoP, cool])
[View query results: query #1, query #2, query #3, query #4, query #5, query #6, query #7]
# Composable fields
Arguments passed to a field can receive other fields or operators as input.
?query=
posts.
if (
hasComments(),
sprintf(
"Post with ID %s has %s comment(s) and title '%s'",
[
id(),
commentCount(),
title()
]
),
sprintf(
"Post with ID %s, created on %s, has no comments",
[
id(),
date(d/m/Y)
]
)
)@postDesc
# Composable fields in directive arguments
Through composable fields, the directive can be evaluated against the object, granting it a dynamic behavior.
The example below implements the standard GraphQL skip directive, however it is able to decide if to skip the field or not based on a condition from the object itself:
/?query=
posts.
title|
featuredimage<
skip(if:isNull(featuredimage()))
>.
src
# Composable directives
A directive can modify the behaviour of another directive. Values can be passed from one to another through "expressions": special variables set by each directive, wrapped with %...%.
For instance, in the example below, directive <forEach> iterates through all the items in an array, passing each of them to its composed directive <applyFunction> through expression %value%.
?query=
echo([
[banana, apple],
[strawberry, grape, melon]
])@fruitJoin<
forEach<
applyFunction(
function: arrayJoin,
addArguments: [
array: %value%,
separator: "---"
]
)
>
>
# Directive expressions
An expression, defined through symbols %...%, is a variable used by directives to pass values to each other. An expression can be pre-defined by the directive or created on-the-fly in the query itself.
In the example below, an array contains strings to translate and the language to translate the string to. The array element is passed from directive <forEach> to directive <advancePointerInArray> through pre-defined expression %value%, and the language code is passed from directive <advancePointerInArray> to directive <translate> through variable %toLang%, which is defined only in the query:
/?query=
echo([
[
text: Hello my friends,
translateTo: fr
],
[
text: How do you like this software so far?,
translateTo: es
],
])@translated<
forEach<
advancePointerInArray(
path: text,
appendExpressions: [
toLang:extract(%value%,translateTo)
]
)<
translate(
from: en,
to: %toLang%,
oneLanguagePerField: true,
override: true
)
>
>
>
# Skip output if null
Exactly the same result above (<skip(if(isNull(...)))>) can be accomplished using the ? operator: Adding it after a field, it skips the output of its value if it is null.
/?query=
posts.
title|
featuredimage?.
src
# Skip argument names
Field and directive argument names can be deduced from the schema.
This query...
/?
postId=1&
query=
post($postId).
date(d/m/Y)|
title<
skip(false)
>
...is equivalent to this query:
/?
postId=1&
query=
post(id: $postId).
date(format: d/m/Y)|
title<
skip(if: false)
>