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

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.Value + ' ' + lastname.Value  + ' ' + age.ToString().Value"

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.Value + ' ' + lastname.Value  + ' ' + age.ToString().Value

"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.Value + ' ' + lastname.Value + ' ' + age.ToString().Value"
    }
  ]

To get the value of a variable in a expression use Value. For example, if you want to capitalize your concatenate variable you can create another variable with expression concatenate.Capitalize().Value or change the value of concatenate variable to firstname.Capitalize().Value + ' ' + lastname.Capitalize().Value + ' ' + age.ToString().Capitalize.Value

For example, these are equal and returns the same:

{
    "name": "firstname",
    "type": "string",
    "expression": true,
    "value": "firstname.ToUpper()"
}

and

{
    "name": "firstname",
    "type": "string",
    "expression": true,
    "value": "firstname.ToUpper().Value"
}

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 = "NOW.Format('20060102150405.000').ReplaceAll('.','').Value"

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

Methods¶

The methods are defined by type of variable, means, methods for int cannot be used for string, a least you convert the returned value, after this, you can use string methods.

For example, with above variables, you can't use for concatenate the expression firstname.Value + ' ' + lastname.Value + ' ' + age.Value because age is an int, you first need to convert to string with ToString() method.

String methods¶

See String methods

Int methods¶

See Int methods

Float methods¶

See Float methods

Bool methods¶

See Bool methods

Datetime methods¶

See Datetime methods

Language definition¶

Dixer v1.x.x uses Expr package for expressions support.

You can see the Language Definition of this version to understand how works. Follow this guide adapted to cases tested in Dixer.

Supported Literals¶

• strings - single and double quotes (e.g. "hello", 'hello')
• numbers - e.g. 103, 2.5, .5
• arrays - e.g. [1, 2, 3]
• booleans - true and false

Supported Operators¶

Expr comes with a lot of operators:

Arithmetic Operators¶

• + (addition)
• - (subtraction)
• * (multiplication)
• / (division)
• % (modulus)
• ** (pow)

Example:

firstname.Value + lastname.Value

Digit separators¶

Integer literals may contain digit separators to allow digit grouping into more legible forms.

Example:

10_000_000_000

Comparison Operators¶

• == (equal)
• != (not equal)
• < (less than)
• > (greater than)
• <= (less than or equal to)
• >= (greater than or equal to)

Logical Operators¶

• not or !
• and or &&
• or or ||

Example:

age.Value < 25 || age.Value > somevar.Value

String Operators¶

• + (concatenation)
• matches (regex match)
• contains (string contains)
• startsWith (has prefix)
• endsWith (has suffix)

To test if a string does not match a regex, use the logical not operator in combination with the matches operator:

not ("foo" matches "^b.+")

You must use parenthesis because the unary operator not has precedence over the binary operator matches.

Example:

'Arthur' + ' ' + 'Dent'

Result will be set to Arthur Dent.

Membership Operators¶

• in (contain)
• not in (does not contain)

Example:

firstname.Value in ["santiago", "perla"]

Numeric Operators¶

• .. (range)

Example:

age.Value in 18..45

The range is inclusive:

1..3 == [1, 2, 3]

Ternary Operators¶

• foo ? 'yes' : 'no'

Example:

age.Value > 30 ? "mature" : "immature"