firstNonNull - Find the first non-null value in the list of arguments

firstNonNull will take a list of arguments and return the first value it finds, in the order of the arguments, that is not null

Note

This will only work on scalar values, like number, string or timestamp. It will not work on objects.

Syntax

Like many functions in DataPrime, firstNonNull supports two notations, function and method notation. These interchangeable forms allow flexibility in how you structure expressions.

Function notation

firstNonNull(value: any, ...values: any): any

Method notation

value: any.firstNonNull(...values: any): any

Arguments

Name	Type	Required	Description
value	any	true	The first argument. Will be checked for a non-null value first
...values	any	true	All subsequent arguments, in order they should be checked

Example - Selecting from unconsistent fields for the same value

Consider the following log documents:

{
    "userId": "123",
    "user_id": null,
    "user_identifier": null
},
{
    "userId": null,
    "user_id": "456",
    "user_identifier": null
},
{
    "userId": null,
    "user_id": null,
    "user_identifier": "789"
}

As we can see, there are multiple different fields in which a user ID can appear. This is a very common situation with logs. Using firstNonNull we can avoid having to painfully consolidate these values, by selecting the first populated field.

Function notation

choose canonical_user_id from firstNonNull(userId, user_id, user_identifier)

Method notation

choose canonical_user_id from userId.firstNonNull(user_id, user_identifier)

This will produce the following documents:

{
    "canonical_user_id": "123"
},
{
    "canonical_user_id": "456"
},
{
    "canonical_user_id": "789"
}

Now each field has the same name, we have created schema on read consistency.

case_lessthan

Next if