README-dev.md

Tricks

Jackson DateTime support

@JsonComponent
class JodaDateTimeSerializer : JsonSerializer<DateTime>() {

    override fun serialize(value: DateTime, gen: JsonGenerator, serializers: SerializerProvider) =
            gen.writeString(JodaUtils.format(value))

}

@JsonComponent
class JodaDateTimeDeserializer : JsonDeserializer<DateTime>() {
    override fun deserialize(p: JsonParser?, ctxt: DeserializationContext?): DateTime =
            JodaUtils.parse(p!!.valueAsString)

}

hateoas

XML support

Simply add this dependency to build.gradle.kts:

implementation("com.fasterxml.jackson.dataformat:jackson-dataformat-xml")

Dynamic exclusion of property in JSON serialization

Goal: in ObjectGroup, choose dynamically whether to return the list of objects or not. Possibilities:

1. As in the first implementation, use ObjectGroup and ObjectGroupExtended. Problem: we need different queries in the repository, hence duplicating a lot of code
2. DTOs: requires a conversion + a lot of repetition in the definition/instantation of them
3. @JsonView. This annotation let us define views, such as Simple and Detailed, and then configure on the go the jackson mapping to use one or the other. Nice, however every nested object need also to to be annotated. Here, it would mean annotate UserGroup, Unit, etc. Overkill since it only concerns one endpoint
4. The cleaner in my opinion: use a JsonFilter. For that, one has to specify on the entity that a filter will be used and then of course create a filter that will exclude the objects properties upon some condition.
5. Annotate the objects field with @field:JsonInclude(JsonInclude.Include.NON_NULL) and set it to null when withObjects is false

Implementation of 3), @JsonView:

interface Views {
    interface Simple
    interface Detailed: Simple
}

// on the Entity (note the @JsonView can be set on a whole class as well)
data class XX (
    @JsonView(Views.Simple::class)
    prop: Int,

    @JsonView(Views.Details::class)
    objects: List<String>
)

// in the controller
val mapping = MappingJacksonValue(xx)
mapping.serializationView = if (withObjects) Views.Detailed::class.java else Views.Simple::class.java
return mapping

Implementation of 4):

// annoate the entity / DTO
@JsonFilter("noObjectsFilter")
data class ObjectGroup(...)

// define a helper function which applies the filter
fun asJacksonMapping(obj: Any, withObjects: Boolean = false): MappingJacksonValue {
   val mapping = MappingJacksonValue(obj)
   // the secret: to NOT ignore any properties, just pass a non-existing property name (_x_)
   mapping.filters = SimpleFilterProvider().addFilter(
           "noObjectsFilter",
           SimpleBeanPropertyFilter.serializeAllExcept(if (withObjects) "_x_" else "objects"))
   return mapping
}

// use it
val ogrpList = objectGroupRepository.findAll()
return asJacksonMapping(ogrpList)

documentation

• do not use the same name for different inner classes representing parameters (e.g. EditableFields), as openapi swagger will get confused

Resources

• repository custom implementations with EntityManager: https://dzone.com/articles/add-custom-functionality-to-a-spring-data-reposito
• native queries in Kotlin: https://blog.trifork.com/2018/08/28/spring-data-native-queries-and-projections-in-kotlin/
• advices on how to use hibernate with Spring/Kotlin (to read!!!): https://kotlinexpertise.com/hibernate-with-kotlin-spring-boot/

TODO

• review endpoints
• provide custom constructors for POJO
• remove Optionals ? in repos
• @RequestAttribute vs @RequestHeader + rethink the auth mechanism
• profiles ?
• use the spring data rest fully (HATEOAS, functions in repository become endpoints) ?
• in values, check the date range in controller + use object creation date to avoid scanning too many month ?
• directly save into cassandra from the input API ?
• add salt to passwords in MySQL !!
• we can delete usergroups, but not users. Users that are part of no groups are useless... ??

Permissions, gosh

• userGroups:
  • any can see the userGroup basic infos /userGroups, /userGroups/{id}
  • users part of the group can see other users /userGroups/{id}/users
  • admins only can modify group (add users, etc.)