Column: expose reference to Column object in init callback

[mielvds]

Hi!

I'm using the init callback function on Column to sanitize some input based on the column's type casting before inserting.

Quick & dirty example:

const column = new pgp.helpers.Column({
            name,
            cast,
            init: (col: [helpers.initCB](https://vitaly-t.github.io/pg-promise/helpers.html#.initCB)) => {
                // Drop invalid date value
                if (col.exists && cast === 'date' && !isValidDate(col.value)) {
                    return null
                }
                return col.value
            },
        })

While this works fine, It might be a nice addtion to allow access to access the Column object from inside init()
Either by (typescript for clarity):

• extending the signature: init: (config: helpers.initCB, column: helpers.Column) => { ... }
• extening helpers.initCB: init: (col: {source: any, name: string, value:any, exists: boolean, column:helpers.Column})

Is this something that can be considered? Would the be a performance hit? Happy to work on a PR

[vitaly-t]

You already have column of type Column in your code. So why not just use that?

[mielvds]

I do, but that means using information outside of the init function. Fine by me, but it's probably less error-prone to avoid this.

[vitaly-t]

In retrospective, I should have passed Column as this into init and others. Instead, this is set to the source, for some forgotten now reasons. Correcting it though would be a breaking change, perhaps now worth doing, unless a major version is impending.

I am still not clear why do you want to access Column from inside the object itself? You didn't specify the reason.

[mielvds]

Because I use Column.cast to check the target datatype and validate the value based on that