Dynamic query criteria

At the moment query criteria is hard coded in the method name, so if we need in some cases to find products by created time starts with, and in another case to find products by created time ends with, we need to have 2 methods.

fun findByCreatedTimeStartsWith(createdTime: DateTime)
fun findByCreatedTimeEndsWith(createdTime: DateTime)

As solution can be dynamic query criteria

sealed class OrderedCriteria<T> {
    class Gt<T>(value: T) : OrderedCriteria // greater than this value
    class Gte<T>(value: T) : OrderedCriteria // greater than or equal to this value
    class Lt<T>(value: T) : OrderedCriteria // less than this value
    class Lte<T>(value: T) : OrderedCriteria // less than or equal to this value
    class Match<T>(value: T) : OrderedCriteria // match the value
    // ...
}

fun findBy(createdTime: OrderedCriteria<DateTime>)
fun countBy(createdTime: OrderedCriteria<DateTime>)

In this case we can have just one method for searching and cover all the cases. This solution is just an alternative way, it doesn’t mean the actual approach should be deleted.

Also, we can add sorting

enum class Sorting {
    ASC, DESC, NONE
}

sealed class OrderedCriteria<T> {
    class Gt<T>(value: T, sort: Sorting = Sorting.NONE) : OrderedCriteria
    // ...
}

And we also can add some annotation to method parameters to configure more specific projection if needed.

[graemerocher]

@raderio Thanks for the feedback, yes a DSL like that would probably be nice and something we can consider in the future. We certainly need a “Criteria”-like API to allow for dynamic queries as well as static queries.

We first want to get the initial support for static queries stable and released however, so this one is definitely on the radar for the future.

[raderio]

This approach is more flexible than Spring Data JPA, where the query is hard-coded in the method name. So if you need to filters entities by created time in some case greater than and in some case less than, we need to have 2 methods, and choose one of depending on that user sends to us.

That I am proposing is to generate a method at compile time that will create the query at run-time based on the parameters passed to this method. In this case, a lot of boilerplate will be eliminated.