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import kotlin.reflect.full.declaredMemberProperties | |
import kotlin.reflect.full.primaryConstructor | |
/** | |
* Merge two data classes | |
* | |
* The resulting data class will contain: | |
* - all fields of `other` which are non null | |
* - the fields of `this` for the fields which are null in `other` | |
* | |
* The function is immutable, the original data classes are not changed | |
* and a new data class instance is returned. | |
* | |
* Example usage: | |
* | |
* val a = MyDataClass(...) | |
* val b = MyDataClass(...) | |
* val c = a merge b | |
*/ | |
infix inline fun <reified T : Any> T.merge(other: T): T { | |
val nameToProperty = T::class.declaredMemberProperties.associateBy { it.name } | |
val primaryConstructor = T::class.primaryConstructor!! | |
val args = primaryConstructor.parameters.associateWith { parameter -> | |
val property = nameToProperty[parameter.name]!! | |
(property.get(other) ?: property.get(this)) | |
} | |
return primaryConstructor.callBy(args) | |
} |
I just tested (also using Kotlin 1.3.41
), all seems to work fine. How are you using it?
Thanks for your response.
Here is my config:
- kotlin_version = '1.3.40'
- classpath 'com.android.tools.build:gradle:3.4.1'
- implementation 'org.jetbrains.kotlin:kotlin-reflect:1.3.41'
REPL:
import com.example.test_only.ProductModel
import com.example.test_only.merge
var apple1 = ProductModel("RED", "APPLE", "SMALL")
var apple2 = ProductModel("GREEN", "APPLE", "BIG")
var apple3 = apple1.merge(apple2)
println("$apple1")
println("$apple2")
println("$apple3")
println("-----")
apple1 = ProductModel("RED", "APPLE", "SMALL")
apple2 = ProductModel("GREEN", "APPLE", "BIG")
apple3 = apple2.merge(apple1)
println("$apple1")
println("$apple2")
println("$apple3")
Output
ProductModel(color=RED, fruit=APPLE, size=SMALL)
ProductModel(color=GREEN, fruit=APPLE, size=BIG)
ProductModel(color=GREEN, fruit=APPLE, size=BIG)
-----
ProductModel(color=RED, fruit=APPLE, size=SMALL)
ProductModel(color=GREEN, fruit=APPLE, size=BIG)
ProductModel(color=RED, fruit=APPLE, size=SMALL)
And what does ProductModel
look like?
I have tried 2 model class:
package com.example.test_only
data class ProductModel(
var color: String?,
var fruit: String?,
var size: String?
)
and
app: build.gradle
androidExtensions {
experimental = true
}
import android.os.Parcelable
import kotlinx.android.parcel.Parcelize
@parcelize
data class ProductModel(
var color: String?,
var fruit: String?,
var size: String?
) : Parcelable
Thanks, now I can reproduce your results. The output looks as expected to me: apple1
and apple2
stay untouched, and apple3
is the merge result of apple1
and apple2
. What would you expect?
What output would you expect for apple3
in your two examples?
Oh finally I got your ideal.
- Stay untouched with
apple1
andapple2
. - Merged object is new object called
apple3
.
import com.example.test_only.ProductModel
import com.example.test_only.merge
var appleOld = ProductModel(null, "APPLE", null, 1)
var appleNew = ProductModel("GREEN", null, "BIG", 2)
var appleMerged = appleOld.merge(appleNew)
println("$appleOld")
println("$appleNew")
println("$appleMerged")
println("-----")
appleOld = ProductModel(null, "APPLE", null, 1)
appleNew = ProductModel("GREEN", null, "BIG", 2)
appleMerged = appleNew.merge(appleOld)
println("$appleOld")
println("$appleNew")
println("$appleMerged")
Output
ProductModel(color=null, fruit=APPLE, size=null, num=1)
ProductModel(color=GREEN, fruit=null, size=BIG, num=2)
ProductModel(color=GREEN, fruit=APPLE, size=BIG, num=2)
ProductModel(color=null, fruit=APPLE, size=null, num=1)
ProductModel(color=GREEN, fruit=null, size=BIG, num=2)
ProductModel(color=GREEN, fruit=APPLE, size=BIG, num=1)
Thanks for your response.
You save me all day.!
Yes indeed :)
Will update update the explanatory comments
We already did it. 👍
hoiulj
I'm merging objects which has inherited properties so I ended up using the following snippet.
Also .associateWith
simplifies the loop a little.
import kotlin.reflect.full.memberProperties
import kotlin.reflect.full.primaryConstructor
inline infix fun <reified T : Any> T.merge(other: T): T {
val nameToProperty = T::class.memberProperties.associateBy { it.name }
val primaryConstructor = T::class.primaryConstructor!!
val args = primaryConstructor.parameters.associateWith { parameter ->
val property = nameToProperty[parameter.name]!!
property.get(other) ?: property.get(this)
}
return primaryConstructor.callBy(args)
}
I was hoping this would work with let's call them deep classes?
data class Some(val a: String?, val b: String?)
data class Other(val some: Some?, val c: String?, val d: String?)
when i do Other(Some("a", null), "c", null).merge(Other(Some(null, "b"), null, "d))
I'd expect to get Other(Some("a", "b"), "c", "d")
It's indeed a shallow merge. Deep merge would be interesting.
@josdejong did you have any solution about. A deep merge would be interesting?
@e-g-hategan I have the same requirement.
i m Doing Single level marge using This Code
inline infix fun <reified T : Any> T.merge(other: T): T {
val nameToProperty = T::class.declaredMemberProperties.associateBy { it.name }
val primaryConstructor = T::class.primaryConstructor!!
val args =
primaryConstructor.parameters.associateWith { parameter ->
val property = nameToProperty[parameter.name]!!
(property.get(other) ?: property.get(this))
}
val mergedObject = primaryConstructor.callBy(args)
nameToProperty.values.forEach { it ->
run {
val property = it as KMutableProperty<*>
val value = property.javaGetter!!.invoke(other) ?: property.javaGetter!!.invoke(this)
property.javaSetter!!.invoke(mergedObject, value)
}
}
return mergedObject
}
How can I add extra condition, for example:
- The resulting data class will contain:
-
- all fields of
other
which are non null or zero
- all fields of
-
- the fields of
this
for the fields which are null or zero inother
- the fields of
or
- The resulting data class will contain:
-
- all fields of
other
which are non null or Double 0.0
- all fields of
-
- the fields of
this
for the fields which are null or Double 0.0 inother
- the fields of
Which line I have to put this kind of conditions?
@talatkuyuk this logic captured in the line:
parameter to (property.get(other) ?: property.get(this))
Right now the behavior is: take the property from other
, but if that is null
, take the property from from this
.
You can adjust the exact behavior of when to pick a property from either other
or this
as you like, i.e. add an extra conditional check to pick other
only when it is non null and not zero (when it is a numeric value).
@josdejong Thank you very much. I understand it, but I am new in Kotlin. I am not familiar with to
operator. I didn't write any inflix function yet. Just I needed this.
- The resulting data class will contain:
-
- all fields of
other
which are non null or non Double with value 0.0
- all fields of
-
- the fields of
this
for the fields which are null or Double with value 0.0 inother
- the fields of
I tried to make it, I am stuck.
Something like this - just change the exact logic to meet your needs (and think through what logic you need for Double, Float, Int. etc, there may be a smart way to check whether any numeric type is zero, I don't know):
infix inline fun <reified T : Any> T.mergeIgnoreZero(other: T): T {
val nameToProperty = T::class.declaredMemberProperties.associateBy { it.name }
val primaryConstructor = T::class.primaryConstructor!!
val args = primaryConstructor.parameters.associateWith { parameter ->
val property = nameToProperty[parameter.name]!!
val valueOther = property.get(other)
val valueThis = property.get(this)
if (valueOther is Double && valueOther == 0.0) {
valueThis
} else {
valueOther ?: valueThis
}
}
return primaryConstructor.callBy(args)
}
@josdejong Thank you very much. It worked.
👍
I use your util with
implementation 'org.jetbrains.kotlin:kotlin-reflect:1.3.41'
But can not receive any merged field. :(