Patch Update Error Handling

[DarrenClarke17]

Hi PA Community, 

I wonder if you can help me I am building an app that will allow people to scan items of stock and update a Dataverse Table to say it has been scanned (to assist with stock take).

I wanted to capture an error if the item didn't exist with in the table, but it is not throwing an error even if the item didn't exist. I would have thought it would of errored if it couldn't find the item in the data source. 

The code for the patch is :

Patch(
    'Reconcile Tables',
    LookUp(
        'Reconcile Tables',
        BatchNo = txtBatchScanned_1.Text
    ),
    {
        'Found at Stocktake': true,
        Location: dpdLocID_1.Selected.LocationID
    }
);
Reset(txtBatchScanned_1)

The code I was using to capture the error is (I know its not in a If Statement I just wanted to see if it was working in a label. 

First(
    Errors(
        'Reconcile Tables'
        )
    )
.Message

I have looked at the PowerApps monitor and these are the actions it is taking 

So my question is if the patch function tries to patch a record in a dataverse table that doesn't exist does it throw an error.

[RandyHayes · Accepted solution]

@DarrenClarke17 

No, it will not error!

You have to realize that a Patch statement "patches" records together...from left to right.

The first parameter (in your case) is the Datasource.  When Patch sees a datasource, it knows it is working with such. (The first parameter can also be just a record).

The main part of updating a record is the primary key.  This is really the only thing that Patch cares about is the primary key.  If there IS a primary key value, then Patch will update.  If there is NO primary key value, then it will create.

So, Patch will then "patch" all the remaining parameters together into one record to determine the above.

The purpose of the LookUp in your formula is to return a record that has that primary key.  Patch will then combine your specified record with the record that is looked up.  So, in a normal situation, if the lookup returns a record, then it will have a primary key and whatever record you then patch that with will also have that primary key...and that is what is passed to the datasource and thus the record is updated.

In your case, if the Lookup returns nothing, then the first record that is patched/combined with the specified record means nothing.  The result of it will be just the specified record...without any primary key.  That then is passed to the datasource and a record created.

So, in your case, if you need to make sure there is a record to patch, then I would do the Lookup prior to the patch...otherwise, state your error if there is not.

Example:

With({_record:     
    LookUp(
        'Reconcile Tables',
        BatchNo = txtBatchScanned_1.Text
    )
    },

    If(IsBlank(_record.BatchNo),
        Notify("No record"), //or whatever you want to do here

        Patch('Reconcile Tables',
            _record,
            {
                'Found at Stocktake': true,
                Location: dpdLocID_1.Selected.LocationID
            }
        )
    )
);
Reset(txtBatchScanned_1)

I hope this is helpful for you.

[DarrenClarke17]

@RandyHayes - Thanks so much this worked, its been baffling me for a couple of hours. I am slowly getting there building powerapps/Solutions, but now and then I just get stumped. 

Just so my brain processes your response, as I have the BatchNo field set to required and is the key of the table, because I am not actually passing this through, Patch just accepts it but as it hits the table as the record doesn't exist it tries to create one but with out the BatchNo it just fails to create? 

[RandyHayes]

@DarrenClarke17 

Not so much...the primary key is not something you provide to create a record (because you cannot set the key usually, that is up to the datasource).  If you provide a blank key to Patch, it will instead "ask" the datasource to create a record.  If you provide the key, then it will "ask" the datasource to update the record.

Your formula should not have failed but instead you should have found new records created from it.

[DarrenClarke17]

@RandyHayes  Ah okay, it was weird as when I was checking the table in dataverse it wasn't showing a record with just location attached it just wasn't showing at all. So I thought it would have been because I wasn't sending a BatchNo through. So are you saying I should have records with just a location and not Batch No? As I thought to create a new record you had to use Defaults('DataSource')  Sorry for another question...

[RandyHayes]

@DarrenClarke17 

You *should* have such records.  Keep in mind though, when referring to the primary key - that is not the primary column...it is the one that is the unique identifier for the table.  The jargon is a little different in the Dataverse!

[DarrenClarke17]

@RandyHayes Just from the *should* tells me that is just another wonderful and mystical thing in the Microsoft Universe that can't really be explained haha. As I have just filtered the data and there is no records with just Location...

But thanks for your help, and the quick responses much appreciated 😀

[RandyHayes]

@DarrenClarke17 

Always little surprises around every corner!!

Happy to help!