Provide options.mergeObjects for easy and correct recursive merging. #5885
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benjamn
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Jan 31, 2020
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benjamn
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Jan 31, 2020
| const merged: any[] = []; | ||
| const authors = new Map<string, any>(); | ||
| function add(author: any) { | ||
| merge(existing: any[], incoming: any[], { readField, mergeObjects }) { |
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Is there any way to easily share complicated examples like this between the documentation and the tests? @trevorblades @hwillson
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@benjamn Great question - I know when @trevorblades added MDX support to the docs, he also opened up the possibility of requiring/importing shared docs. I'm not sure if we can reach outside of the docs project to pull from the AC codebase though, so I'll defer to Trevor for an answer.
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@hwillson Any idea what's up with that Codecov report? #5885 (comment) @StephenBarlow Tagged you for review because this involved additional changes to the most recent docs about merging non-normalized data. Happy to answer questions tomorrow / next week! |
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One of the benefits of #5880 is that any custom
mergefunction gets to see itsincomingdata before any nestedmergefunctions have been run, somergefunctions have full control over how the contents of their input arguments get combined, in principle.In practice, it's actually pretty tricky to implement a correct custom
mergefunction that might encounter any non-normalized data, because even non-normalized objects can have custommergefunctions for their fields, which must be called.We've been (briefly) recommending that people ignore this edge case and simply return
{ ...existing, ...incoming }when combining non-normalized objects, so that no fields are lost. However, this style ignores the possibility that theexistingandincomingobjects might have totally different__typenames, risks combining{ __ref }objects with non-reference objects, and does not invoke any nestedmergefunctions. A rat's nest of edge cases!This PR introduces a general-purpose
options.mergeObjectshelper function to enable easy and correct merges ofexistingandincomingvalues. It also comes in handy when merging specific elements from two arrays, which is something the cache cannot do automatically.