Patch just the fields that has changed

[at711]

I need to Patch my Sharepoint List based on 50+ text/radio/dropdown inputs in my canvas app. Because there may be more than one user simultaneously changing the same record, I want to only Patch the fields that the user actually changed.

First, I tried to keep a single Record variable "varModifiedValues" to keep track of modified changes.

For every user input, I have something like this inside OnChange -

// Field A Text Input OnChange
Set(varModifiedValues,
  First( // get first record in the temp table
    AddColumns(
      DropColumns( // drop the column first so that it doesn't error out with 'column already exists'
        Table(varModifiedValues), // create temp table from the record variable
        "FieldA" // column to drop
      ),
      "FieldA",
      Self.Text
    )
  )
);

 This variable is a Record with only modified fields.

In the Save function, I tried to do this -

// Patch existing row; currSystemID is a variable that holds the ID of this row
Patch(System, LookUp(System, ID=currSystemID), varModifiedValues);

But this causes red squiggly line on Patch, saying "The specified column 'FieldA' does not exist. The column with the most similar name is 'FieldA'"

I've read in couple of places that using a variable to do a Patch may be problematic.

I can bite the bullet and do a Patch by specifying every field one by one for my 50+ inputs, but then I don't know how to NOT include the ones that did not change.

//assuming FieldA changed but FieldB didn't;

Patch(System, LookUp(System, ID=currSystemID),
  {
    'FieldA': varModifiedValues.FieldA, // this is ok
    'FieldB': varModifiedValues.FieldB // but this will overwrite FieldB with empty value because FieldB was never changed
  }

Is there a way to do something like 

Patch...
  {
   If(!IsBlank(varModifiedValues.FieldA), 'FieldA': varModifiedValues.FieldA) //only patch if value changed
  }

Or even better approach than what I have?

Hopefully I've explained my issue well enough. Thank you in advance.

[SebS]

@at711 

You can do something like this:

Patch(System, LookUp(System, ID=currSystemID),

{
FieldA:If(Lookup(System, ID = currSystemID, FiledA) = varModifiedValues.FieldA,Lookup(System, ID = currSystemID, FiledA), varModifiedValues.FieldA)
}

)

So this will look into the data source and pull this Field to Match it with the variable. If both are Blank, then they will stay blank, but if one of them is a different Variable will overwrite it. It will cost your performance but it should work.

[at711]

Thank you for your response.

So I think your logic says - 

//if sharepoint list FieldA = varModifiedValues.FieldA, use the value in sharepoint list

// else use varModifiedValues.FieldA

If Sharepoint List FieldA already has a value "Hello World" and the user does not change FieldA in the app, wouldn't it update Field A to blank, since varModifiedValues.FieldA is blank and it is different from SP list FieldA?

[SebS]

@at711 

Sorry Yes You are right forgot abut this one 🙂

Patch(System, LookUp(System, ID=currSystemID),

{
FieldA:If(Lookup(System, ID = currSystemID, FiledA) = varModifiedValues.FieldA || IsBlank(varModifiedValues.FieldA),Lookup(System, ID = currSystemID, FiledA), varModifiedValues.FieldA)
}

)

[SebS · Accepted solution]

@at711 

You need to check Blank first 🙂

Patch(System, LookUp(System, ID=currSystemID),

{
FieldA:If(IsBlank(varModifiedValues.FieldA) || Lookup(System, ID = currSystemID, FiledA) = varModifiedValues.FieldA,Lookup(System, ID = currSystemID, FiledA), varModifiedValues.FieldA)
}

)

[at711]

Thank you, that would seem to work, although as you said I'm concerned about the performance.

I am a little baffled that this is the only working way to Patch things in Power Apps.

This question also suggests that you cannot use any dynamic name with Patch - 
https://powerusers.microsoft.com/t5/Building-Power-Apps/Patching-to-a-SharePoint-list-column-without...

Hopefully Power Apps reaches the level of maturity to do things like this soon.