Gelly Reference 

Built-in data types 

Gelly supports literals for a variety of built-in data types that you can use in your expressions. The syntax is very similar to JavaScript, so you can usually use the same syntax to declare literals as you might in JS within Gelly snippets.

Integers and Numbers are written out as the digits of the number:

query {
  anInteger: 5
  aDecimal: 10.5
}

Booleans are written as true or false:

query {
  yes: true
  no: false
}

Strings are written with the characters between double quotes, and using \" to escape quote characters within the string:

query {
  aString: "foo"
  withAQuoteInIt: "when she said \"yes\", it was incredible!"
}

DateTimes are written using the timestamp function which accepts a timestamp string as input, or the date function which accepts a date string as input. The date string is formatted according to Postgres' timestamp and date literal syntax, which is documented in the Postgres docs. If not specified, times are assumed to be in UTC.

query {
  aTimestamp: timestamp("2021-05-01 15:00:00")
  anISO8601Date: timestamp("2021-05-01T15:00:00Z")
  aDate: date("2021-05-01")
}

nulls are written as null. There's no undefined in Gelly.

Arrays are written between square brackets with commas (,) separating the elements.

query {
  someNumbers: [1, 2, 3]
  someStrings: ["foo", "bar", "baz"]
  myStuff: [1, "foo", true, null]
}

Objects are written between curly brackets with the keys on the left-hand side of a colon (:) and commas (,) separating the elements.

query {
  anObject: {foo: "bar", baz: true}
}

Built-in operators 

Gelly has a number of built-in operators for arithmetic, comparison, and boolean logic.

Boolean logic 

Prefix a boolean expression with an exclamation mark to inverse the boolean value.

query {
  !false # returns true
}

Test if two booleans are both true with &&, or if either boolean is true with ||

1query {
2  true && true # returns true
3  true && false # returns false
4  true || false # returns true
5  false || false # returns false
6}

Equality and inequality 

Test if two expressions are equal with two equals signs, like ==.

1query {
2  1 == 1 # returns true
3  1 == 2 # returns false
4  true == true # returns true
5  true == false # returns false
6}

Test if two expressions are not equal with !=.

1query {
2  1 != 1 # returns false
3  1 != 2 # returns true
4  true != true # returns false
5  true != false # returns true
6}

Numeric ordering 

Test how two numbers relate to each other with >, >=, <, and <=.

query {
  1 > 1 # returns false
  1 >= 1 # returns true
  10 > 1 # returns true
}

Arithmetic 

Add, subtract, multiply or divide numbers with +, -, *, or /:

query {
  1 + 1 # returns 2
  2 * 10 # returns 10
  10 / 2 # returns 5
}

query {
  10 / 3 # returns 3.3 repeating
}

Use the % operator for a modulus (integer division remainder).

query {
  10 % 3 # returns 1
}

Boolean functions 

isNull(<value:> Any): Boolean! 

Returns true if the passed value is null, and false otherwise.

query {
  isNull(null) # returns true
  isNull({apple: "red"}.apple) # returns false
  isNull({apple: "red"}.orange) # returns true
}

String functions 

concat(<string:> [String!]!, delimiter: String): String! 

Returns a new string built by stringing each input string together, optionally with a delimiter.

query {
  concat(["Hello", "", "world!"])
}

query {
  posts {
    details: concat([title, " by ", author.name])
  }
}

query {
  posts {
    details: concat(tags, delimiter: ", ")
  }
}

leftSlice(<string:> String!, length: Number): String! 

Returns a substring of the input string, starting from the first (left most) character position and including length characters after.

query {
  leftSlice("foobar", length: 3) # returns "foo"
}

length(<string:> String!): Integer! 

Returns the number of characters in the passed string.

query {
  length("foobar") # returns 6
}

lower(<string:> String!): String! 

Returns the lower-cased version of the input string.

query {
  lower("FooBar") # returns "foobar"
}

rightSlice(<string:> String!, length: Number): String! 

Returns a substring of the input string, starting from the last (right most) character position and including length previous characters.

query {
  rightSlice("foobar", length: 3) # returns "bar"
}

slice(<string:> String!, start: Number = 0, length: Number): String! 

Returns a substring of the input string, starting from the start character position, or the first character if no start is passed, and going length characters further, or to the end of the string if length is not passed.

query {
  slice("foobar", length: 3) # returns "foo"
}

The start character position is inclusive, so start: 0 would include the first character in the string onwards, or start: 1 would skip the first character but include the second character onwards.

query {
  slice("foobar", start: 2, length: 3) # returns "oba"
}

If the start argument is provided and the length argument isn't provided, the remainder of the string from the start position is returned.

query {
  slice("foobar", start: 4) # returns "ar"
}

upper(<string:> String!): String! 

Returns the upper-cased version of the input string.

query {
  upper("FooBar") # returns "FOOBAR"
}

JSON functions 

contains(<value:> JSON!, item: (String | JSON)!): Boolean! 

Returns true if the given item is a subset of the given JSON value, and false otherwise. The value to be searched must be a JSON object or array, and the item can be a JSON object, array, string, or number. Corresponds to the @> operator in Postgres.

contains can be used to check if a JSON object contains a subset of another JSON object:

query {
  contains({ foo: "bar", other: true }, item: { foo: "bar" }) # returns true, as the item is a subset of the value
}

contains can be used to check if an array contains an item:

query {
  contains(["a", "b", "c"], item: "a") # returns true, as "a" is contained within the array
}

contains can be used to check if an object has a key:

query {
  contains({foo: "1"}, item: "foo") # returns true, as the object has the foo key
  contains({foo: "1"}, item: "bar") # returns false, as the object doesn't have the foo key
}

Aggregation functions 

The where argument 

All aggregate functions in Gelly take a where argument which allows for filtering the set of records for passing through the function. The where argument doesn't filter the returned set of records, or affect other function calls, it only affects the aggregate function to which it is passed. where is a convenient way of quickly filtering records without having to filter the whole record set, but can be used interchangeably with the where relational command.

Using where with the count function allows counting records that match certain criteria.

query {
  posts {
    count(id, where: isPublished)
  }
}

This is equivalent to running count with a [where] relational command.

1query {
2  posts {
3    count(id)
4    [where isPublished]
5  }
6}

Notably, the where argument can be used to issue multiple aggregate calls at once with different filter conditions without having to do many outer selection sets. The [where] relational command filters all records before passing them onto the functions, so all aggregate functions in a selection set are given the same, already filtered list of records to aggregate.

1query {
2  posts {
3    totalCount: count(id)
4    publishedCount: count(id, where: isPublished)
5    highScoreCount: count(id, where: score > 10)
6    bannedCount: count(id, where: author.banned)
7  }
8}

avg(<number:> Number!, where: Boolean): Number! 

Averages the given field number across the aggregated set, optionally filtered to only consider values that pass the where condition.

1query {
2  posts {
3    avg(score)
4    [group by author.name]
5  }
6}

To do a filtered average easily, you can use the where argument to the avg function.

query {
  posts {
    avg(score, where: isPublished)
  }
}

every(where: Boolean): Boolean! 

Returns true if all the passed values are true themselves, or false if any of the passed values are falsy.

query {
  posts {
    every(published)
  }
}

To check if a subset of records match the passed conditions, use a where relational command.

1query {
2  posts {
3    every(score > 10)
4    [where published]
5  }
6}

count(<value:> Any, where: Boolean): Integer! 

Counts the number of non-null values across the aggregated set, optionally filtered to only consider values which pass the where condition.

query {
  posts {
    count(id)
  }
}

To do a filtered count easily, you can use the where argument to the count function.

query {
  posts {
    count(id, where: isPublished)
  }
}

count is also subject to the relational commands for the query, so you can filter a count aggregate as well as other aggregates at the same time.

1query {
2  posts {
3    count(id)
4    avg(score)
5    [where published]
6  }
7}

max(<number:> Number!, where: Boolean): Number! 

Finds the maximum value of the number argument across the aggregated set, optionally filtered to only consider values which pass the where condition.

1query {
2  posts {
3    max(score)
4    [group by author.name]
5  }
6}

To find the maximum value in a subset of records easily, you can use the where argument to the max function.

query {
  posts {
    max(score, where: isPublished)
  }
}

min(<number:> Number!, where: Boolean): Number! 

Finds the minimum value of the number argument across the aggregated set, optionally filtered to only consider values which pass the where condition.

1query {
2  posts {
3    min(score)
4    [group by author.name]
5  }
6}

To find the minimum value in a subset of records easily, you can use the where argument to the min function.

query {
  posts {
    min(score, where: isPublished)
  }
}

sum(<number:> Number!, where: Boolean): Number! 

Adds the value of the number argument together across the whole aggregated set, optionally adding only values which pass the where condition.

1query {
2  posts {
3    sum(voteCount)
4    [group by author.name]
5  }
6}

To sum only the value from a subset of records easily, you can use the where argument to the sum function.

query {
  posts {
    max(score, where: isPublished)
  }
}

Time functions 

date(input: String!): DateTime! 

Create a DateTime object from an input string representing a date (without a time). Uses the Postgres date and time formatting syntax -- see more details in the Postgres docs.

query {
  date("2021-05-05")
}

1query {
2  posts {
3    id
4    publishAt
5    [where publishAt > date("2021-05-05")]
6  }
7}

datePart(part: String!, date: DateTime!): Number! 

Retrieve a given component of a DateTime object, like the year, week, or minutes. Uses the Postgres syntax for the date part, and returns it as a number. The valid parts are century, day, decade, dow (day of week), doy (day of year), epoch, hour, isodow, isoyear, microseconds, millennium, milliseconds, minute, month, quarter, second, week, year.

See more details about date_part in the Postgres docs.

query {
  datePart("year", date("2021-05-05"))
}

1query {
2  posts {
3    id
4    publishDay: datePart("dow", publishAt)
5  }
6}

dateTrunc(part: String!, date: DateTime!): DateTime! 

Rounds down a DateTime object to closest date part. Uses the Postgres syntax for the date part. The valid parts are microseconds, milliseconds, second, minute, hour, day, week, month, quarter, year, decade, century, millennium.

See more details about date_trunc in the Postgres docs.

query {
  dateTrunc("month", now())
}

interval(input: String!): Interval! 

Create a Interval object from an input string representing a specific duration of time. Intervals are useful for doing math with dates. interval uses the Postgres interval formatting syntax -- see more details in the Postgres docs.

query {
  short: interval("5 minutes")
  long: interval("1 year")
  longer: interval("1 year") + interval("6 months")
}

1query {
2  posts {
3    id
4    publishAt
5    [where publishAt > now() - interval("60 days")]
6  }
7}

now(): DateTime! 

Gets the current system time from the Gelly server.

query {
  now()
}

1query {
2  posts {
3    id
4    publishAt
5    [where publishAt > now()]
6  }
7}

1query {
2  posts {
3    id
4    publishAt
5    [where publishAt > now()]
6  }
7}

timestamp(input: String!): DateTime! 

Create a DateTime object from an input string representing a specific point in time. Uses the Postgres time formatting syntax -- see more details in the Postgres docs. If not specified, times are assumed to be in UTC.

query {
  timestamp("2021-05-05 10:10:00")
}

1query {
2  posts {
3    id
4    publishAt
5    [where publishAt > timestamp("2021-05-01T15:00:00Z")]
6  }
7}

Numeric functions 

abs(<number:> Number!): Integer! 

Gets the absolute value of a given input number.

query {
  abs(-10) # returns 10
  abs(10) # returns 10
}

ceil(<number:> Number!): Integer! 

Returns the nearest integer greater than or equal to the input number.

1query {
2  ceil(2.5) # returns 3
3  ceil(3) # returns 3
4  ceil(-2.5) # returns -2
5  ceil(-1) # returns -1
6}

floor(<number:> Number!): Integer! 

Returns the nearest integer less than or equal to the input number.

1query {
2  floor(2.5) # returns 2
3  floor(3) # returns 3
4  floor(-2.5) # returns -3
5  floor(-1) # returns -1
6}

exp(<number:> Number!): Number! 

Returns the exponential (the constant e raised to the given power) of the input number.

query {
  exp(1) # returns 2.7182818284590452
}

ln(<number:> Number!): Number! 

Returns the natural logarithm (the logarithm with base e) of the input number.

query {
  ln(1) # returns 0
  ln(10) # returns 2.302585092994046
}

log(<number:> Number!, base: Number = 10): Number! 

Returns the logarithm with base base of the input number. The base defaults to 10.

query {
  log(10) # returns 1
  log(10, base: 2) # returns 0.1505149978319906
}

mod 

There is no mod function in Gelly. Instead, use the % operator.

power(<number:> Number!, exponent: Number!): Number! 

Returns the given number raised to the given exponent.

query {
  power(10, exponent: 3) # returns 100
  power(2, exponent: 5) # returns 32
}

round(<number:> Number!, precision: Number = 0): Number! 

Rounds the given fractional number to the nearest number of decimal places, counted by precision. Precision defaults to 0, so when not passed round rounds to an integer number.

1query {
2  round(1) # returns 1
3  round(1.11111) # returns 1
4  round(1, precision: 2) # returns 1
5  round(1.11111, precision: 2) # returns 1.11
6}

sign(<number:> Number!): Number! 

Returns 1 if the number is positive, -1 if the number is negative, or 0 if the number is 0.

sqrt(<number:> Number!): Number! 

Returns the square root of the given number.

query {
  sqrt(4) # returns 2
  sqrt(10) # returns 3.162277660168379
}

trunc(<number:> Number!, precision: Number = 0): Number! 

Truncates the given fractional number to the number of decimal places counted by precision. trunc doesn't do any rounding, precision is simply discarded, so if you want to round the number, see round. precision defaults to 0.

1query {
2  trunc(1) # returns 1
3  trunc(1.11111) # returns 1
4  trunc(1.111111, precision: 2 # returns 1.11
5  trunc(1, precision: 2) # returns 1
6}

random(): Number! 

Returns a random number greater than or equal to 0 and less than 1.

Trigonometric functions and constants 

acos(<number:> Number!): Number! 

Returns the inverse cosine of the input number given in radians, output in radians.

asin(<number:> Number!): Number! 

Returns the inverse sine of the input number given in radians, output in radians.

atan(<number:> Number!): Number! 

Returns the inverse tangent of the input number given in radians, output in radians.

cos(<number:> Number!): Number! 

Returns the cosine of the input number given in radians, output in radians.

cot(<number:> Number!): Number! 

Returns the cotangent of the input number given in radians, output in radians.

degrees(<radians:> Number!): Number! 

Converts the given input radians in radians to degrees.

pi 

Returns the value of pi, accurate to 15 decimal places.

radians(<degrees:> Number!): Number! 

Converts the given input degrees in degrees to radians.

sin(<number:> Number!): Number! 

Returns the sine of the input number given in radians, output in radians.

tan(<number:> Number!): Number! 

Returns the tangent of the input number given in radians, output in radians.

Type conversion functions 

cast(<input:> Any!, type: String!): Any! 

Converts an input expression to a new type if possible. Can fail if the value of the input can't be converted. Expects the destination type's name to be passed as a string literal, and only accepts values from the table of type names below.

Available type names:

query {
  cast(1, type: "String") # returns "1"
  cast(-42, type: "String") # returns "-42"
}

query {
  cast("1", type: "Number") # returns 1
  cast("-42", type: "Number") # returns -42
  cast("apple", type: "Number") # will throw an error as the string can't be converted
}

Note: null values are not changed when casting in Gelly. casting null always returns null.

Other functions 

coalesce(<input:> [Any!]!>): Any! 

query {
  coalesce([null, 1, 2]) # returns "1"
}

Returns the first non-null value in the array.