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Anonymous's avatar
Anonymous
Not applicable
5 years ago

Storing value in variable, so it can be referenced without reevaluation

Hi!   let URL = "MyRestApiGetQuery", Source = if try Web.Contents(URL)[HasError]=true and Web.Contents(URL)[Error]="text that equates to true",                     then "error identified",     ...
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Jimmy801's avatar
Jimmy801
Community Champion
5 years ago

Hello Anonymous 

 

you can do like this and store the complete result in a variable, but probably is quering the website twice also here, because of lazy evaluation of M

let

URL = "MyRestApiGetQuery",

QueryWEB= try Web.Contents(URL)


in

if QueryWEB[HasError]=true then 
    if QueryWEB[Error]="text that equates to true" then

                    then "error identified",

                    else  "something else"
else null //When nor error was identified


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Have fun

Jimmy

 

  • Anonymous's avatar
    Anonymous
    Not applicable
    5 years ago

    Thanks!

     

    I abused a random joke generating API https://official-joke-api.appspot.com/random_joke 

     

    If the calls were done through a variable, like in your code, then the contents of the variable would never change and so I think the query was run only once

     

    If the calls were done 'naked', then they would often but not always have the same contents, leading me to believe the query was ran multiple times. The results of second below query are kind of mysterious

     

    let
    URL = "https://official-joke-api.appspot.com/random_joke",
    Jokesetup = Json.Document(Web.Contents(URL))[setup],
    Jokeoutput =
    Jokesetup&Jokesetup&Jokesetup&Jokesetup&Jokesetup&Jokesetup&Jokesetup&Jokesetup&Jokesetup&Jokesetup

    // to 100 -- jokesetup is always the same

    in Jokeoutput

     

    vs

     

    let

    URL = "https://official-joke-api.appspot.com/random_joke",

     

    Jokeoutput =
    Json.Document(Web.Contents(URL))[setup]&Json.Document(Web.Contents(URL))[setup]&Json.Document(Web.Contents(URL))[setup]&Json.Document(Web.Contents(URL))[setup]&Json.Document(Web.Contents(URL))[setup]&Json.Document(Web.Contents(URL))[setup]

    // - to 100, result of Web.Contents vary, but hard to figure out what is going on. The server should return a 4xx error if 100 requests are received from same ISP in 15 minutes, but above code will work even with 150 Web.Contents. It seems some under the hood power query features kick in after 10 or so W.C() and the same result is returned for the remainder of W.C()'s

    in Jokeoutput