Expressions¶

Expressions are used to change the value of a variable, to skip rows matched for avoid load in destination for dataflow and to use in your dataflow mapping like columns sources.

Create a variable with expression value¶

To create a variable that is value is a expression, set the key expression to true.

Expressions returns the followed types:

• string
• int
• float
• bool
• datetime
• map

Example to create a variable that returns a expression concatenating three variables values:

[[variables]]
name = 'firstname'
type = 'string'
value = 'santiago'

[[variables]]
name = 'lastname'
type = 'string'
value = 'de la cruz'

[[variables]]
name = 'age'
type = 'int'
value = '28'

[[variables]]
name = 'concatenate'
type = 'string'
expression = true
value = "firstname + ' ' + lastname  + ' ' + toString(age)"

variables:
  - name: firstname
    type: string
    value: santiago
  - name: lastname
    type: string
    value: de la cruz
  - name: age
    type: int
    value: 28
  - name: concatenate
    type: 'string'
    expression: true
    value: firstname + ' ' + lastname  + ' ' + toString(age)

"variables": [
    {
      "name": "firstname",
      "type": "string",
      "value": "santiago"
    },
    {
      "name": "lastname",
      "type": "string",
      "value": "de la cruz"
    },
    {
      "name": "age",
      "type": "int",
      "value": "28"
    },
    {
      "name": "concatenate",
      "type": "string",
      "expression": true,
      "value": "firstname + ' ' + lastname + ' ' + toString(age)"
    }
  ]

Call variable with expression in other expression with Render method¶

To call a variable that holds a expression in other variable that is a expression too, use the method Render, Example: variable_name.Render.

Use case¶

Save a custom datetime format in a variable and call it in other expressions. Example:

[[variables]]
name = 'customnow'
type = 'string'
expression = true
value = "replaceAll(NOW.Format('20060102150405.000'), '.', '')"

[[variables]]
name = 'logFileName'
expression = true
type = 'string'
value = "log' + '-' + customnow.Render + '.txt'"

Builtin functions¶

See: Builtin functions

Language definition¶

Dixer uses Expr package for expressions support.

You can see the Language Definition of this version to understand how works. Below the content:

Literals¶

Operators¶

Examples:

user.Age in 18..45 and user.Name not in ["admin", "root"]

foo matches "^[A-Z].*"

Membership Operator¶

Fields of structs and items of maps can be accessed with . operator or [] operator. Elements of arrays and slices can be accessed with [] operator. Negative indices are supported with -1 being the last element.

The in operator can be used to check if an item is in an array or a map.

user.Name in list["available-names"]

Optional chaining¶

The ?. operator can be used to access a field of a struct or an item of a map without checking if the struct or the map is nil. If the struct or the map is nil, the result of the expression is nil.

author?.User?.Name

Nil coalescing¶

The ?? operator can be used to return the left-hand side if it is not nil, otherwise the right-hand side is returned.

author?.User?.Name ?? "Anonymous"

Slice Operator¶

The slice operator [:] can be used to access a slice of an array.

For example, variable array is [1, 2, 3, 4, 5]:

array[1:4] == [2, 3, 4]
array[1:-1] == [2, 3, 4]
array[:3] == [1, 2, 3]
array[3:] == [4, 5]
array[:] == array

Built-in Functions¶

all(array, predicate)¶

Returns true if all elements satisfies the predicate. If the array is empty, returns true.

all(Tweets, {.Size < 280})

any(array, predicate)¶

Returns true if any elements satisfies the predicate. If the array is empty, returns false.

one(array, predicate)¶

Returns true if exactly one element satisfies the predicate. If the array is empty, returns false.

one(Participants, {.Winner})

none(array, predicate)¶

Returns true if all elements does not satisfy the predicate. If the array is empty, returns true.

map(array, predicate)¶

Returns new array by applying the predicate to each element of the array.

filter(array, predicate)¶

Returns new array by filtering elements of the array by predicate.

count(array, predicate)¶

Returns the number of elements what satisfies the predicate. Equivalent to:

len(filter(array, predicate))

len(v)¶

Returns the length of an array, a map or a string.

abs(v)¶

Returns the absolute value of a number.

int(v)¶

Returns the integer value of a number or a string.

int("123") == 123

float(v)¶

Returns the float value of a number or a string.

Predicate¶

The predicate is an expression that accepts a single argument. To access the argument use the # symbol.

map(0..9, {# / 2})

If items of the array is a struct or a map, it is possible to access fields with omitted # symbol (#.Value becomes .Value).

filter(Tweets, {len(.Value) > 280})

Braces { } can be omitted:

filter(Tweets, len(.Value) > 280)