Question

How come number parameter can be fetched, but string parameter can't be fetched in JSONTemplator

T
Badge +3

I encountered something peculiar and I was wondering how/why this is the case.

 

When I build a JSON document, I am able to fetch a number parameter, and parse that to a string.

When I however try to do the same with a text parameter, and try to parse that to a string, I get an error. See below:

image Also seems related to this old community thread. In some sense I get the error 'undeclared variable' (since in XQuery the '$' is used for variables), but it seems odd that this error does occur for a text parameter and not for a number parameter, and I was wondering how that is possible.

 

Of course there are easy solutions. I generally try to enclose user parameters in double quotes in these situations, like e.g. 

{
    "key": "$(IN_Text)"
}

In that case, (data type parsing) functions also can be used, like e.g. 

{
    "key": xs:string("$(IN_Text)")
}

But in this case that's a bit of a redundant example, as without that data type parsing function, the parameter is already inserted as a string.

 

Just as a caution to other users, similar to the XQuery function 'get-attribute("")' (that's automatically used when you double click on an attribute from the menu), there is also the XQuery function 'fme:parameter-value("")'. but this one has an active issue that it is not aware of the context in which it is used. More particulary, when used in a custom transformer, the 'fme:parameter-value("")' function doesn't work correctly (C662869, FMEENGINE-70950).

 

Then of course there is also the easy option of converting the parameters to attributes with e.g. a ParameterFetcher, but although effective, I think it's not such a clean solution (as you already have the information as a parameter). Also, in case you have one execution of a Custom Transformer, and within it you end up with many more features/records, it always seems a bit inefficient to me to spread out this constant parameter value over all of your features/records.

 

So long story short, I would advise to use the double quotes workaround in the meantime ;)

 

 

 

2 replies

takashi
Rank
Userlevel 2
Badge +17

$(IN_Text) written in a template expression will be replaced with the parameter value as-is when running the workspace.

 

If the parameter value was abc for example,

{ "key" : $(IN_Text) }

will be interpreted as

{ "key" : abc }

and it's apparently incorrect as a JSON document. It's the reason for the error.

 

{ "key" : "abc" }

is intended, you therefore need to write this expression if the parameter value could be a non-numeric representation.

{ "key" : "$(IN_Text)" }

T
Badge +3

$(IN_Text) written in a template expression will be replaced with the parameter value as-is when running the workspace.

 

If the parameter value was abc for example,

{ "key" : $(IN_Text) }

will be interpreted as

{ "key" : abc }

and it's apparently incorrect as a JSON document. It's the reason for the error.

 

{ "key" : "abc" }

is intended, you therefore need to write this expression if the parameter value could be a non-numeric representation.

{ "key" : "$(IN_Text)" }

Hi @Takashi Iijima​ 

 

Tnx again for sharing your insight.

I know that { "key" : abc } is invalid JSON, which is why in my JSONTemplator I used the xs:string() xQuery function to attemt to parse the value to a string, i.e. I had { "key": xs:string($(IN_Text)) }

 

I guess I was confused by the error "context item": undeclared variable. Because of the term 'variable' I thought it had something to do that the user parameter $(IN_Text) would be misinterpreted for an xQuery variable $VARIABLE.

 

But I just ran some additional checks.

'$(IN_Text)' = 'abc'

{ "key": xs:string($(IN_Text)) } --> ERROR: "context item": undeclared variable

 

'$(IN_Text)' = '1'

{ "key": xs:string($(IN_Text)) } --> { "key": "1" } (thus this works, and the issue was indeed in the text value)

 

And also without a reference to the parameter I get this error:

{ "key": xs:string(abc) } --> ERROR: "context item": undeclared variable

{ "key": abc } --> ERROR: "context item": undeclared variable

 

Thus I think the main thing here was my own misinterpretation of the error message. Thanks for your insight which led me in this direction

 

 

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