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Dynamics 365 Community / Forums / Microsoft Dynamics AX (Archived) / Difference between fet...
Microsoft Dynamics AX (Archived)

Difference between fetchmode and firstonly in datasource

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Posted on by Community Member

In datasource object of query (i.e query of report) there are two properties:

fetchmode

firstonly

I have a case like this:

datasource1 need to retrieve only one record.

datasource2 is after datasource1, and related to datasource1 with exists join.

Only if the relation between datasource1+datasource2 is ok, then data shall be retrieved,

but what if when query is selected - the first record fetch doesn't have data related for datasource2 (existjoin is false), but the second record (of datasource2) has related data.

I need to do the query, that the fetchmode or firstonly will influence after check the whole query as the example (and not fetching the datasource1, and then check for existence for datasource2), so I need to know - what is the major difference between 'fetchmode' and 'firstonly'.

 

Thanks :)

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  • Suggested answer
    Ivan (Vanya) Kashperuk Profile Picture
    Ivan (Vanya) Kashperuk on at

    FetchMode and FirstOnly are completely unrelated and different settings.

    Maybe you meant? FirstFast?

    FetchMode can be either 1:1 or 1:n. 1:n was used in reports previously, but should generally be avoided going forward. I won't therefore go into trying to explain how it works. 1:1 however is ensuring a regular join like you'd see in SQL.

    FirstOnly will only return the 1 record.

    Your explanation was a bit messy so I am not sure I got your question right, but if you have 2 datasources, DS1 and DS2, where the link is an exists join, that is identical to

    select TOP 1 DS1 where exists (select from DS2 on A=B)

    So you will only get the first available DS1 record where DS2 also exists

  • Community Member Profile Picture
    Community Member on at

    OK - if firstfast parsed to some sql, it's fine with me.

    If not (when something in AX that fetched the first datasource, and then the second), then logically it will be wrong.

    i.e : ds2 has 2 records for same record of ds1, and only the second record match for exist join.

    Thanks

  • Verified answer
    Ivan (Vanya) Kashperuk Profile Picture
    Ivan (Vanya) Kashperuk on at

    The query keywords are in fact passed in as hints to SQL query planner.

    Ignore what I asked about FirstFast - that does not seem to be related to your question.

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