ADF Expression Generator

Generate Azure Data Factory expressions for common scenarios.

Task

Create valid ADF expressions based on the described requirement.

Arguments

• $ARGUMENTS: Description of what the expression should do
  • Example: yesterday's date in yyyy-MM-dd format
  • Example: partition path like year=2025/month=01/day=15
  • Example: first day of current month
  • Example: extract filename from full path
  • Example: check if weekday
  • Example: conditional SQL query based on parameter

Expression Syntax Rules

Basic Syntax

• Expressions start with @ prefix
• Use @{expression} for string interpolation
• Nested functions: @function1(function2(value))

Expression vs String Interpolation

// Full expression (returns typed value)
"value": "@utcnow()"

// String interpolation (returns string)
"value": "Date is @{utcnow()}"

// Explicit expression type
{
  "value": "@concat('prefix_', pipeline().parameters.Name)",
  "type": "Expression"
}

Common Expression Patterns

Date/Time

Yesterday's Date:

@formatDateTime(adddays(utcnow(), -1), 'yyyy-MM-dd')

First Day of Month:

@formatDateTime(startOfMonth(utcnow()), 'yyyy-MM-dd')

Last Day of Previous Month:

@formatDateTime(adddays(startOfMonth(utcnow()), -1), 'yyyy-MM-dd')

Date Partition Path (year/month/day):

@concat(
  formatDateTime(utcnow(), 'yyyy'), '/',
  formatDateTime(utcnow(), 'MM'), '/',
  formatDateTime(utcnow(), 'dd')
)

Hive Partition Path:

@concat(
  'year=', formatDateTime(pipeline().parameters.ProcessDate, 'yyyy'),
  '/month=', formatDateTime(pipeline().parameters.ProcessDate, 'MM'),
  '/day=', formatDateTime(pipeline().parameters.ProcessDate, 'dd')
)

Is Weekday Check:

@and(greater(dayOfWeek(utcnow()), 0), less(dayOfWeek(utcnow()), 6))

N Days Ago:

@formatDateTime(adddays(utcnow(), -7), 'yyyy-MM-dd')

String Operations

Extract Filename from Path:

@substring(
  variables('FilePath'),
  add(lastIndexOf(variables('FilePath'), '/'), 1),
  sub(length(variables('FilePath')), add(lastIndexOf(variables('FilePath'), '/'), 1))
)

Remove File Extension:

@substring(
  item().name,
  0,
  lastIndexOf(item().name, '.')
)

Build Dynamic Table Name:

@concat(pipeline().parameters.Schema, '.', pipeline().parameters.Table)

Safe Property Access:

@coalesce(activity('Lookup').output.firstRow.Value, 'default')

Conditional Logic

Conditional SQL Query:

@if(
  equals(pipeline().parameters.FullLoad, true),
  'SELECT * FROM dbo.Table',
  concat('SELECT * FROM dbo.Table WHERE Date >= ''', pipeline().parameters.LastDate, '''')
)

Conditional File Path:

@if(
  equals(pipeline().parameters.Environment, 'prod'),
  'production/data/',
  'development/data/'
)

Collections

Array to Comma-Separated String:

@join(activity('Lookup').output.value, ',')

Check Array Not Empty:

@greater(length(activity('Lookup').output.value), 0)

Get First N Items:

@take(activity('Lookup').output.value, 10)

Skip First N Items:

@skip(activity('Lookup').output.value, 10)

Pipeline/Activity References

Current Pipeline Info:

@pipeline().Pipeline          // Pipeline name
@pipeline().DataFactory       // Data factory name
@pipeline().RunId             // Current run ID
@pipeline().TriggerName       // Trigger name
@pipeline().TriggerType       // 'Manual', 'Schedule', 'Tumbling'

Activity Output:

@activity('LookupConfig').output.firstRow.ColumnName
@activity('CopyData').output.rowsCopied
@activity('CopyData').output.rowsRead
@activity('WebCall').output.Response

Tumbling Window:

@trigger().outputs.windowStartTime
@trigger().outputs.windowEndTime

Blob Event Trigger:

@trigger().outputs.body.fileName
@trigger().outputs.body.folderPath

ForEach Item Access

Inside ForEach:

@item()                       // Current item
@item().tableName             // Property access
@item()['property-with-dash'] // Bracket notation for special chars

Format Specifiers

Specifier	Output	Example
yyyy	4-digit year	2025
yy	2-digit year	25
MM	2-digit month	01
M	Month (no zero)	1
MMMM	Full month	January
dd	2-digit day	15
d	Day (no zero)	15
dddd	Full day	Wednesday
HH	24-hour	14
hh	12-hour	02
mm	Minutes	30
ss	Seconds	45
tt	AM/PM	PM
fff	Milliseconds	123

Output Format

Provide:

1. The complete expression
2. Example output value
3. Where to use it (parameter, activity property, etc.)
4. Any caveats or limitations