Handling errors

Errors in Power Query generally halt query evaluation and display a message to the user.

Throwing an error with the error expression

Throwing an error in Power Query is as simple as invoking the error expression.

let
    Source = "foo",
    Output = error "error message"
in
    Output

An example of an Expression.Error error message

The Error.Record function can be used for more control.

let
    Source = "foo",
    Output = error Error.Record("error reason", "error message", "error detail")
in
    Output

An example of an Expression.Error error message with more details

Catching an error with try and otherwise

The try expression converts values and errors into a record value that indicates whether the try expression handled an error or not, as well as the proper value of the error record.

If no error is found, the following record is returned from the try expression:

try "foo"

HasError false with value

If an error is found, the following record is returned from the try expression:

try "foo"+1

HasError true with error record

The Error record contains Reason, Message, and Detail fields.

Content of error record

Depending on the error, the Detail field may contain additional information.

The otherwise clause can be used with a try expression to perform some action if an error occurs:

try "foo"+1 otherwise "There was an error"

is a more compact form of:

result = try "foo"+1,
if result[HasError] then "There was an error" else result[Value]