assert()

Checks for a condition. If the condition is false, outputs error messages and fails the query.

Syntax

assert(condition, message)

Arguments

• condition: The conditional expression to evaluate. If the condition is false, the specified message is used to report an error. If the condition is true, it returns true as an evaluation result. Condition must be evaluated to constant during the query analysis phase.
• message: The message used if assertion is evaluated to false. The message must be a string literal.

Note

condition must be evaluated to constant during the query analysis phase. In other words, it can be constructed from other expressions referencing constants, and can't be bound to row-context.

Returns

• true - if the condition is true
• Raises semantic error if the condition is evaluated to false.

Examples

The following query defines a function checkLength() that checks input string length, and uses assert to validate input length parameter (checks that it's greater than zero).

let checkLength = (len:long, s:string)
{
    assert(len > 0, "Length must be greater than zero") and
    strlen(s) > len
};
datatable(input:string)
[
    '123',
    '4567'
]
| where checkLength(len=long(-1), input)

Running this query yields an error: assert() has failed with message: 'Length must be greater than zero'

Example of running with valid len input:

let checkLength = (len:long, s:string)
{
    assert(len > 0, "Length must be greater than zero") and strlen(s) > len
};
datatable(input:string)
[
    '123',
    '4567'
]
| where checkLength(len=3, input)

input
4567