Adding cdevents tag name for copying struct fields

[rjalander]

This PR includes the changes to add cdevents tag name for CDEvents Subject and Context fields, this will help in copying the struct fields directly from any other source event to CDEvents type event, even the field names are different by using libraries like copygen.

//Source Event
type ProjectCreatedEvent struct {
	ProjectName string `cdevents:"name"`
	RepoURL string `cdevents:"url"`
}

//Destination Event
type RepositoryCreatedCDEvent struct {
	Name string `cdevents:"name"`
	Url string `cdevents:"url"`
}

Note:

1. With this change If anyone using cdevents tag names and in future any of the field name changed, it will be a breaking change for the current users.(They need to update the tag name as per the change)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.94%. Comparing base (f8b8b91) to head (b82880a).

Additional details and impacted files

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##             main      #82   +/-   ##
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  Coverage   79.94%   79.94%           
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  Files          48       48           
  Lines        3291     3291           
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  Hits         2631     2631           
  Misses        552      552           
  Partials      108      108           

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[afrittoli]

Thanks for this @rjalander - I'm a bit at a loss about how this will beneficial, since the mapping between objects and json is already in the json tags. Do you have an example of how this would be used?

Also, it would be nice if to update the code, you can run make generate for that.

[afrittoli]

Is there some implied naming convention to map a field name and position in the json structure to a string?
So that context.source becomes context_source?

[rjalander]

no, but just to differentiate subject's source with the context's source. Keeping tag name as context_source here and for subject's source using it as subject_source

[afrittoli]

The info in the cdevents tag is already in the json tag - I'm not sure I understand the value of adding them to a new tag. Also, this tag here has a different name structure compared to those in the context.

[rjalander]

yes, we tried using json tag info for copygen, but the same json tag will also be used for serialize/deserialize and this will create a problem in matching the field names for different sources,

For Example the source ProjectCreated Gerrit event,

type ProjectCreated struct {
	ProjectName string `json:"projectName" cdevents:"name"`
	HeadName    string `json:"headName" cdevents:"subject_id"`
	Type           string  `json:"type"`
	EventCreatedOn float64 `json:"eventCreatedOn"`
	RepoURL        string  `json:"repoURL,omitempty" cdevents:"context_source"`
}

here the json tag names projectName, headName are used to serialize gerrit event.

[afrittoli]

I think I'm missing some context or maybe knowledge about copygen to better understand what's going on.

I understand that json tag in types that represent Gerrit events is used to marshal/unmarshal gerrit events to JSON - that's the standard way of doing JSON marshalling/unmarshalling in go.

I guess cdevents tag is meant to tell copygen that it should fill the field of a struct with the CDEvents field specified in the tag. What I don't understand is why we need to add cdevents tags on the CDEvents SDK side.

[rjalander]

Actually the same tag should be present in all the structs(Gerrit + CDEvents) to match fields and generate functions to copy fields from Gerrit event to CDEvent.
So we need to have a tag names on CDEvents SDK and the same tag names can be used to match different source events, which can be translated into CDEvents.

An example from copygen shows model struct copied into domain struct, https://github.com/switchupcb/copygen/tree/main/examples/tag#example-tag