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#228: Declare dependency on json4s optional (#245)
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* #228: Declare dependency on json4s optional

* Add to README
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saeltz authored Mar 2, 2023
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58 changes: 42 additions & 16 deletions README.md
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[![Maven Central](https://img.shields.io/maven-central/v/io.moia/teleproto_2.13.svg)](https://search.maven.org/search?q=teleproto_2.13)

The tele**proto** library reduces the boilerplate required to map case classes generated from [Protofiles](https://developers.google.com/protocol-buffers/docs/proto3)
The tele**proto** library reduces the boilerplate required to map case classes generated
from [Protofiles](https://developers.google.com/protocol-buffers/docs/proto3)
using [ScalaPB](https://github.com/scalapb/ScalaPB) to corresponding version-independent business model case classes.

The library is intended for the use case outlined below:
* An application/service works on an evolving *business model* with some semantics.

* An application/service works on an evolving *business model* with some semantics.
* *Protofiles* model the transfer of that business model in the current and previous version.
* *ScalaPB* is used to generate case classes for the protocol buffers model.
* *ScalaPB* is used to generate case classes for the protocol buffers model.

![Image showing relationships between Messages and Classes](documentation/messages-classes.svg)

Depending on the specific use case it is necessary to define readers and/or writers to convert between the business model
Depending on the specific use case it is necessary to define readers and/or writers to convert between the business
model
and the current or a previous protocol buffers model.
Reading/writing for the current protocol buffers model should be straightforward.
Reading/writing a previous model should reflect similar semantics regarding the current business model.

To use the library, add the following to your `build.sbt`:

```sbt
libraryDependencies += "io.moia" %% "teleproto" % "2.3.0"
```

If you also want to be able to write to (`VersionedModelWriter.toJson`) and read from (`VersionedModelReader.fromJson`)
JSON, you have to add the following dependency to your project as well:

```sbt
libraryDependencies += "com.thesamet.scalapb" %% "scalapb-json4s" % "0.12.1"
```

**For now** the library supports mapping of matching models and therefore for the parts of models that have not changed
in an evolution. That reduces the code required to support previous versions (and a lot of code to support the current version, too...).
in an evolution. That reduces the code required to support previous versions (and a lot of code to support the current
version, too...).

## Mapping DSL

The library defines abstractions for both directions: `Reader[PROTO, MODEL]` and `Writer[MODEL, PROTO]`.
Readers/writers are converters between the business model and Protocol Buffers model from the business model user's perspective.
Readers/writers are converters between the business model and Protocol Buffers model from the business model user's
perspective.

It is assumed that a writer can never fail and if it fails it fails with a **5xx Internal Server Error**.
But a client cannot be trusted and therefore a `Reader[PROTO, MODEL]` produces either a `PbSuccess(model: MODEL)` or a
Expand Down Expand Up @@ -174,19 +192,23 @@ object Result {
```

**Please note:**

* The generated code is much larger and the code above is reduced to the important part of the structure.
* There is no relationship between `Result.Error` and `Result.Success` in PB since they are just plain messages.
The only connection is defined by the `oneof` which results in the classes of the `trait Calculation`.
* Since everything is somewhat optional in PB an `Empty` object is added to the trait by ScalaPB.

The reader/writer macros can map the generated objects/traits/case classes to the business model trait (and its case
classes). The reader will reject `Empty` with a `PbFailure` and read the content of the other two constructors.
Similar to the mapping of case classes the reader/writer requires implicit readers/writers for the inner types (`Error` and `Success`).
Similar to the mapping of case classes the reader/writer requires implicit readers/writers for the inner types (`Error`
and `Success`).
One can either define them or let the macro generate them, too.

**Please note:** This will not work for recursive trait types. case objects would be empty messages and are also not supported.
**Please note:** This will not work for recursive trait types. case objects would be empty messages and are also not
supported.

Example usage:

```
sealed trait Calculation
case class Error(message: String) extends Calculation
Expand All @@ -205,9 +227,10 @@ implicit val calculationWriter: Writer[Calculation, v1.Calculation] = ProtocolBu
## Special Mappings

The `Reader`/`Writer` companions already define some conversions:
* `BigDecimal` in business model, `String` in PB

* `BigDecimal` in business model, `String` in PB
* `Instant` in business model, `Timestamp` in PB
* ... *(look into the source code)*
* ... *(look into the source code)*

If a mapping generation is not possible one has to define reader/writer programmatically.
Usually, a mapping cannot be generated for generic types in the business model due to the *impedance
Expand Down Expand Up @@ -237,9 +260,10 @@ case class SomeModel( case class SomeModel(
}
```

* `taxRate` is surplus in the input, ignored in the mapping and declares the mapping to be *backward compatible*.
* `lastUpdate` is missing in the input but is optional, will be set to `None` and declares the mapping to be *backward compatible*.
* `comment` is missing in the input but has a default value and declares the mapping to be *backward compatible*.
* `taxRate` is surplus in the input, ignored in the mapping and declares the mapping to be *backward compatible*.
* `lastUpdate` is missing in the input but is optional, will be set to `None` and declares the mapping to be *backward
compatible*.
* `comment` is missing in the input but has a default value and declares the mapping to be *backward compatible*.
* `correlationId` is missing in the input, is not optional, has no default value and causes the whole reader to be
considered *incompatible*.

Expand All @@ -254,7 +278,7 @@ cause a writer to be incompatible.

Generating a backward/forward compatible reader/writer using the macro will raise a **warning**.
Annotations `@backward("signature")` and `@forward("signature")` (signatures are explained in the warning) will remove
the warning.
the warning.

The support of migrations is currently limited to implicit readers/writers of old Protocol Buffers types to the new
business model wherever possible.
Expand All @@ -263,7 +287,8 @@ the model that actually changed.

## License

This code is open source software licensed under the [Apache 2.0 License](http://www.apache.org/licenses/LICENSE-2.0.html).
This code is open source software licensed under
the [Apache 2.0 License](http://www.apache.org/licenses/LICENSE-2.0.html).

## Publishing (for maintainers)

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```
sbt +publishSigned
```
Note that your Sonatype credentials need to be configured on your machine and you need to have access writes to publish artifacts to the group id `io.moia`.
Note that your Sonatype credentials need to be configured on your machine and you need to have access writes to
publish artifacts to the group id `io.moia`.
3. Release artifact to Maven Central with:
```
sbt +sonatypeRelease
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32 changes: 17 additions & 15 deletions build.sbt
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Expand Up @@ -15,16 +15,16 @@ lazy val `teleproto` = project
.settings(Project.inConfig(Test)(sbtprotoc.ProtocPlugin.protobufConfigSettings): _*)
.settings(
name := "teleproto",
version := "2.2.1",
version := "2.3.0",
versionScheme := Some("early-semver"),
libraryDependencies ++= Seq(
library.scalaPB % "protobuf;compile",
library.scalaPBJson % Compile,
library.scalaPBJson % "compile;optional",
library.scalaTest % Test,
library.scalaTestPlusCheck % Test,
library.scalaCheck % Test,
"org.scala-lang.modules" %% "scala-collection-compat" % "2.9.0",
"org.scala-lang" % "scala-reflect" % (ThisBuild / scalaVersion).value
library.scalaCollectionCompat,
"org.scala-lang" % "scala-reflect" % (ThisBuild / scalaVersion).value
)
)

Expand All @@ -34,19 +34,21 @@ lazy val `teleproto` = project

lazy val library = new {
object Version {
val scalaPB = scalapb.compiler.Version.scalapbVersion
val scalaPBJson = "0.12.1"
val scalaCheck = "1.17.0"
val scalaTest = "3.2.15"
val scalaTestPlusCheck = "3.2.2.0"
val scapeGoat = "2.1.1"
val scalaPB = scalapb.compiler.Version.scalapbVersion
val scalaPBJson = "0.12.1"
val scalaCheck = "1.17.0"
val scalaTest = "3.2.15"
val scalaTestPlusCheck = "3.2.2.0"
val scapeGoat = "2.1.1"
val scalaCollectionCompat = "2.9.0"
}

val scalaPB = "com.thesamet.scalapb" %% "scalapb-runtime" % Version.scalaPB
val scalaPBJson = "com.thesamet.scalapb" %% "scalapb-json4s" % Version.scalaPBJson
val scalaCheck = "org.scalacheck" %% "scalacheck" % Version.scalaCheck
val scalaTest = "org.scalatest" %% "scalatest" % Version.scalaTest
val scalaTestPlusCheck = "org.scalatestplus" %% "scalacheck-1-14" % Version.scalaTestPlusCheck
val scalaPB = "com.thesamet.scalapb" %% "scalapb-runtime" % Version.scalaPB
val scalaPBJson = "com.thesamet.scalapb" %% "scalapb-json4s" % Version.scalaPBJson
val scalaCheck = "org.scalacheck" %% "scalacheck" % Version.scalaCheck
val scalaTest = "org.scalatest" %% "scalatest" % Version.scalaTest
val scalaTestPlusCheck = "org.scalatestplus" %% "scalacheck-1-14" % Version.scalaTestPlusCheck
val scalaCollectionCompat = "org.scala-lang.modules" %% "scala-collection-compat" % Version.scalaCollectionCompat
}

// *****************************************************************************
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