I have the following linq query:
var test = vendorContact.vendorContactItem
.Where(x => x.ItemNumber == vendorContactItem.Item_Number)
.FirstOrDefault();
It fails on this piece of code, "Value cannot be null, parameter name: source" ... yet it also displays, in the local variables window, "test" as a variable with all its properties populated.
vendorContact.VendorContactItem is null. Presumably this would be the first element to be added to the list. So how is "test" evaluating correctly while simultaneously throwing up that error?
I'm new to Linq, so excuse me if this is an obvious question.
If this is in a loop test in the locals window contains the last value of test, from the last iteration of the loop.
Edit: This has really nothing to do with LINQ, but how the debugger works.
Related
I've seen the JSON array questions here and I'm still a little lost, so could use some extra help.
Here's the setup:
My Flow calls a sproc on my DB and that sproc returns this JSON:
{
"ResultSets": {
"Table1": [
{
"OrderID": 9518338,
"BasketID": 9518338,
"RefID": 65178176,
"SiteConfigID": 237
}
]
},
"OutputParameters": {}
}
Then I use a PARSE JSON action to get what looks like the same result, but now I'm told it's parsed and I can call variables.
Issue is when I try to call just, say, SiteConfigID, I get "The output you selected is inside a collection and needs to be looped over to be accessed. This action cannot be inside a foreach."
After some research, I know what's going on here. Table1 is an Array, and I need to tell PowerAutomate to just grab the first record of that array so it knows it's working with just a record instead of a full array. Fair enough. So I spin up a "Return Values to Virtual Power Agents" action just to see my output. I know I'm supposed to use a 'first' expression or a 'get [0] from array expression here, but I can't seem to make them work. Below are what I've tried and the errors I get:
Tried:
first(body('Parse-Sproc')?['Table1/SiteConfigID'])
Got: InvalidTemplate. Unable to process template language expressions in action 'Return_value(s)_to_Power_Virtual_Agents' inputs at line '0' and column '0': 'The template language function 'first' expects its parameter be an array or a string. The provided value is of type 'Null'. Please see https://aka.ms/logicexpressions#first for usage details.'.
Also Tried:
body('Parse-Sproc')?['Table1/SiteconfigID']
which just returns a null valued variable
Finally I tried
outputs('Parse-Sproc')?['Table1']?['value'][0]?['SiteConfigID']
Which STILL gives me a null-valued variable. It's the worst.
In that last expression, I also switched the variable type in the return to pva action to a string instead of a number, no dice.
Also, changed 'outputs' in that expression for 'body' .. also no dice
Here is a screenie of the setup:
To be clear: the end result i'm looking for is for the system to just return "SiteConfigID" as a string or an int so that I can pipe that into a virtual agent.
I believe this is what you need as an expression ...
body('Parse-Sproc')?['ResultSets']['Table1'][0]?['SiteConfigID']
You can see I'm just traversing down to the object and through the array to get the value.
Naturally, I don't have your exact flow but if I use your JSON and load it up into Parse JSON step to get the schema, I am able to get the result. I do get a different schema to you though so will be interesting to see if it directly translates.
I have this piece of code:
Db.DbDataSet.Tables["costallocations"]
.AsEnumerable()
.Where(Row => Row.Field<long>("callocid") == OldCostAllocationId)[0]["newid"]
And I'm getting the error above. In my opinion, it should work. How can I access the first record of the result set? There will be always only one hit, btw, therefore I use the 0.
I'm trying to get certain keys from the Request.Form.AllKeys string array by using the following:
var result = keys.Where(key => key.StartsWith("added"));
The result is "The name 'result' does not exist in the current context" no matter what I do.
I've also tried:
var result = (from keys in Request.Form.AllKeys
where keys.StartsWith("added")
select keys).ToArray();
Same thing.
I'm new to Linq and Lambda expressions and all, so please forgive the ignorance.
Regards,
Jacques
I found the answer to my question: Delayed execution.
When I actually executed the code and then followed it up by using result.Any() the expression was executed and turned out the correct results.
I'm banging my head against the wall on this one. I was looking at some old database reporting code written in VB6 and came across this line (the code is moving data from a "source" database into a reporting database):
rsTarget!VehYear = Trim(Str(rsSource!VehYear))
When rsSource!VehYear is Null, the above line generates an "Invalid use of Null" run-time error. If I break on the above line and type the following in the Immediate pane:
?rsSource!VehYear
It outputs Null. Fine, that makes sense. Next, I try to reproduce the error:
?Str(rsSource!VehYear)
I get an "Invalid use of Null" error.
However, if I type the following into the Immediate window:
?Str(Null)
I don't get an error. It simply outputs Null.
If I repeat the same experiment with Trim() instead of Str(), everything works fine. ?Trim(rsSource!VehYear) returns Null, as does ?Trim(Null). No run-time errors.
So, my question is, how can Str(rsSource!VehYear) possibly throw an "Invalid use of Null" error when Str(Null) does not, when I know that rsSource!VehYear is equal to Null?
Update: If I type the following in the Immediate window, it works as expected (no error occurs):
?Str(rsSource!VehYear.Value)
This outputs Null. Now, I know that rsSource!VehYear is actually an ADODB.Field instance, but Value is its default property, so Str should be operating on the Value property (which is Null). Even the error message ("Invalid use of Null") suggests that Str is receiving a Null parameter, but how can it treat Null differently in one case and not the other?
My only guess is the internal implementation of Str() is somehow failing to get the default property, and the "Invalid use of Null" error is happening for a different reason (something other than the parameter is causing the "Invalid use of Null", perhaps when it is trying to retrieve the default property from the Field object).
Does anyone have a more detailed, technical explanation for what is actually happening here?
In short:
?Str(rsSource!VehYear)
throws an "Invalid use of Null" error when rsSource!VehYear is Null, but
?Str(rsSource!VehYear.Value)
returns Null.
However, both Trim(rsSource!VehYear) and Trim(rsSource!VehYear.Value) return Null.
If you need a value other than a string, try using IsNull instead:
rsTarget!VehYear = IIf(IsNull(rsSource!VehYear), 0, rsSource!VehYear)
' Note 0 is the default value
The Str function will specifically check if a Null value is passed in and deal with it accordingly. When you pass in an object it attempts to convert the result of a default method to a String. The result of the default method is not passed into the Str method, but Field object is, so a check for the initial Null will fail. The Str function will continue to check the parameter type for datatypes that it supports when it realizes that it has an object, it will attempt to retrieve the default value. It doesn't re-attempt to deal with the default value as it did with the passed in argument, so the attempt to return a Null as a String will fail. It seems MS didn't expect a default value to be Null or any other invalid value for Str. For instance Str doesn't support an empty string either.
This was my workaround in the vb6-days:
rsTarget!VehYear = Trim(Str(rsSource!VehYear & ""))
the & "" will make sure there is allways at least an empty string to work with.
From memory, null database fields are Nothing (or possibly vbNull), which do not have the same rules applied to them as Null. You should just be able to do a quick check:
If (rsSource!VehYear Is Nothing) Then
' Null
Else
' Not null
End If
I'm trying to find the correct names for these 2 "types" of coding expressions in LINQ so that I can refer to them correctly. I want to say that the first is called "Fluent Style"?
var selectVar = arrayVar.Select( (a,i) => new { Line = a });
var selectVar =
from s in arrayVar
select new { Line = s };
First - calling an extension method.
This style of coding is called "fluent interface" as you mentioned.
Second method is called language integrated query
The name of the second form is "query comprehesion syntax", which the compiler translates into the first form.
The first isn't even really LINQ, it's a lambda expression, with a type invariant object created.
(a) => new { blah = b}
The second is a LINQ query filling an on the fly class that has a property Line.
There is no hashrocket operator in this one, so this one is just plain old linq.