Add custom implementations for toString, equals and hashCode (#1480)

Author: cmelchior

CHANGELOG.md

@@ -1,9 +1,29 @@
 ## 1.11.0-SNAPSHOT (YYYY-MM-DD)
 
 ### Breaking Changes
-* None.
+* `BaseRealmObject.equals()` has changed from being identity-based only (===) to instead return `true` if two objects come from the same Realm version. This e.g means that reading the same object property twice will now be identical. Note, two Realm objects, even with identical values will not be considered equal if they belong to different versions.
+
+```
+val childA: Child = realm.query<Child>().first().find()!!
+val childB: Child = realm.query<Child>().first().find()!!
+
+// This behavior is the same both before 1.11.0 and before
+childA === childB // false
+
+// This will return true in 1.11.0 and onwards. Before it will return false
+childA == childB
+
+realm.writeBlocking { /* Do a write */ }
+val childC = realm.query<Child>().first().find()!!
+
+// This will return false because childA belong to version 1, while childC belong to version 2.
+// Override equals/hashCode if value semantics are wanted.
+childA == childC
+```
 
 ### Enhancements
+* Realm model classes now generate custom `toString`, `equals` and `hashCode` implementations. This makes it possible to compare by object reference across multiple collections. Note that two objects at different versions will not be considered equal, even 
+if the content is the same. Custom implementations of these methods will be respected if they are present. (Issue [#1097](https://github.com/realm/realm-kotlin/issues/1097)) 
 * Support for performing geospatial queries using the new classes: `GeoPoint`, `GeoCircle`, `GeoBox`, and `GeoPolygon`. See `GeoPoint` documentation on how to persist locations. (Issue [#1403](https://github.com/realm/realm-kotlin/pull/1403))
 * Support for automatic resolution of embedded object constraints during migration through `RealmConfiguration.Builder.migration(migration: AutomaticSchemaMigration, resolveEmbeddedObjectConstraints: Boolean)`. (Issue [#1464](https://github.com/realm/realm-kotlin/issues/1464)
 * [Sync] Add support for customizing authorization headers and adding additional custom headers to all Atlas App service requests with `AppConfiguration.Builder.authorizationHeaderName()` and `AppConfiguration.Builder.addCustomRequestHeader(...)`. (Issue [#1453](https://github.com/realm/realm-kotlin/pull/1453))

packages/library-base/src/commonMain/kotlin/io/realm/kotlin/internal/RealmObjectHelper.kt

@@ -17,16 +17,20 @@
 package io.realm.kotlin.internal
 
 import io.realm.kotlin.UpdatePolicy
+import io.realm.kotlin.VersionId
 import io.realm.kotlin.dynamic.DynamicMutableRealmObject
 import io.realm.kotlin.dynamic.DynamicRealmObject
 import io.realm.kotlin.ext.asRealmObject
+import io.realm.kotlin.ext.isManaged
+import io.realm.kotlin.ext.isValid
 import io.realm.kotlin.ext.toRealmDictionary
 import io.realm.kotlin.ext.toRealmList
 import io.realm.kotlin.ext.toRealmSet
 import io.realm.kotlin.internal.dynamic.DynamicUnmanagedRealmObject
 import io.realm.kotlin.internal.interop.ClassKey
 import io.realm.kotlin.internal.interop.CollectionType
 import io.realm.kotlin.internal.interop.MemAllocator
+import io.realm.kotlin.internal.interop.ObjectKey
 import io.realm.kotlin.internal.interop.PropertyKey
 import io.realm.kotlin.internal.interop.PropertyType
 import io.realm.kotlin.internal.interop.RealmInterop
@@ -39,6 +43,7 @@ import io.realm.kotlin.internal.interop.RealmValue
 import io.realm.kotlin.internal.interop.Timestamp
 import io.realm.kotlin.internal.interop.getterScope
 import io.realm.kotlin.internal.interop.inputScope
+import io.realm.kotlin.internal.platform.identityHashCode
 import io.realm.kotlin.internal.platform.realmObjectCompanionOrThrow
 import io.realm.kotlin.internal.schema.ClassMetadata
 import io.realm.kotlin.internal.schema.PropertyMetadata
@@ -1145,6 +1150,66 @@ internal object RealmObjectHelper {
         }
     }
 
+    @Suppress("unused") // Called from generated code
+    // Inlining this functions somehow break the IntelliJ debugger, unclear why?
+    internal fun realmToString(obj: BaseRealmObject): String {
+        // This code assumes no race conditions
+        val schemaName = obj::class.realmObjectCompanionOrNull()?.io_realm_kotlin_className
+        val fqName = obj::class.qualifiedName
+        return obj.realmObjectReference?.let {
+            if (obj.isValid()) {
+                val id: RealmObjectIdentifier = obj.getIdentifier()
+                val objKey = id.objectKey.key
+                val version = id.versionId.version
+                "$fqName{state=VALID, schemaName=$schemaName, objKey=$objKey, version=$version, realm=${it.owner.owner.configuration.name}}"
+            } else {
+                val state = if (it.owner.isClosed()) {
+                    "CLOSED"
+                } else {
+                    "INVALID"
+                }
+                "$fqName{state=$state, schemaName=$schemaName, realm=${it.owner.owner.configuration.name}, hashCode=${obj.hashCode()}}"
+            }
+        } ?: "$fqName{state=UNMANAGED, schemaName=$schemaName, hashCode=${obj.hashCode()}}"
+    }
+
+    @Suppress("unused", "ReturnCount") // Called from generated code
+    // Inlining this functions somehow break the IntelliJ debugger, unclear why?
+    internal fun realmEquals(obj: BaseRealmObject, other: Any?): Boolean {
+        if (obj === other) return true
+        if (other == null || obj::class != other::class) return false
+
+        other as BaseRealmObject
+
+        if (other.isManaged()) {
+            if (obj.isValid() != other.isValid()) return false
+            return obj.getIdentifierOrNull() == other.getIdentifierOrNull()
+        } else {
+            // If one of the objects are unmanaged, they are only equal if identical, which
+            // should have been caught at the top of this function.
+            return false
+        }
+    }
+
+    @Suppress("unused", "MagicNumber") // Called from generated code
+    // Inlining this functions somehow break the IntelliJ debugger, unclear why?
+    internal fun realmHashCode(obj: BaseRealmObject): Int {
+        // This code assumes no race conditions
+        return obj.realmObjectReference?.let {
+            val isValid: Boolean = obj.isValid()
+            val identifier: RealmObjectIdentifier = if (it.isClosed()) {
+                RealmObjectIdentifier(ClassKey(-1), ObjectKey(-1), VersionId(0), "")
+            } else {
+                obj.getIdentifier()
+            }
+            val realmPath: String = it.owner.owner.configuration.path
+            var hashCode = isValid.hashCode()
+            hashCode = 31 * hashCode + identifier.hashCode()
+            hashCode = 31 * hashCode + realmPath.hashCode()
+            hashCode
+        } ?: identityHashCode(obj)
+    }
+
     private fun checkPropertyType(
         obj: RealmObjectReference<out BaseRealmObject>,
         propertyName: String,

packages/library-base/src/commonMain/kotlin/io/realm/kotlin/internal/RealmObjectUtil.kt

@@ -142,9 +142,15 @@ internal fun BaseRealmObject.getIdentifier(): RealmObjectIdentifier {
         val classKey: ClassKey = metadata.classKey
         val objKey: ObjectKey = RealmInterop.realm_object_get_key(objectPointer)
         val version: VersionId = version()
-        return Triple(classKey, objKey, version)
+        val path: String = owner.owner.configuration.path
+        return RealmObjectIdentifier(classKey, objKey, version, path)
     } ?: throw IllegalStateException("Identifier can only be calculated for managed objects.")
-    ULong
+}
+
+public fun BaseRealmObject.getIdentifierOrNull(): RealmObjectIdentifier? {
+    return runIfManaged {
+        getIdentifier()
+    }
 }
 
 /**

packages/library-base/src/commonMain/kotlin/io/realm/kotlin/internal/RealmUtils.kt

@@ -48,10 +48,15 @@ import kotlin.reflect.KProperty1
 // `equals` method, which in general just is the memory address of the object.
 internal typealias UnmanagedToManagedObjectCache = MutableMap<BaseRealmObject, BaseRealmObject> // Map<OriginalUnmanagedObject, CachedManagedObject>
 
-// For managed realm objects we use `<ClassKey, ObjectKey, Version>` as a unique identifier
+// For managed realm objects we use `<ClassKey, ObjectKey, Version, Path>` as a unique identifier
 // We are using a hash on the Kotlin side so we can use a HashMap for O(1) lookup rather than
 // having to do O(n) filter with a JNI call for `realm_equals` for each element.
-internal typealias RealmObjectIdentifier = Triple<ClassKey, ObjectKey, VersionId>
+public data class RealmObjectIdentifier(
+    val classKey: ClassKey,
+    val objectKey: ObjectKey,
+    val versionId: VersionId,
+    val path: String
+)
 internal typealias ManagedToUnmanagedObjectCache = MutableMap<RealmObjectIdentifier, BaseRealmObject>
 
 /**

packages/library-base/src/commonMain/kotlin/io/realm/kotlin/internal/platform/SystemUtils.kt

@@ -145,3 +145,8 @@ public expect fun <K : Any?, V : Any?> returnType(field: KMutableProperty1<K, V>
  * Returns whether or not we are running on Windows
  */
 public expect fun isWindows(): Boolean
+
+/**
+ * Returns the identity hashcode for a given object.
+ */
+internal expect fun identityHashCode(obj: Any?): Int

packages/library-base/src/jvm/kotlin/io/realm/kotlin/internal/platform/SystemUtils.kt

@@ -124,3 +124,5 @@ private fun preparePath(directoryPath: String) {
 }
 
 public actual fun isWindows(): Boolean = OS_NAME.contains("windows", ignoreCase = true)
+
+internal actual fun identityHashCode(obj: Any?): Int = System.identityHashCode(obj)

packages/library-base/src/nativeDarwin/kotlin/io/realm/kotlin/internal/platform/SystemUtils.kt

@@ -29,6 +29,7 @@ import platform.Foundation.dataWithContentsOfFile
 import platform.Foundation.timeIntervalSince1970
 import platform.posix.memcpy
 import platform.posix.pthread_threadid_np
+import kotlin.native.identityHashCode
 import kotlin.reflect.KMutableProperty1
 import kotlin.reflect.KType
 
@@ -192,3 +193,5 @@ private fun NSData.toByteArray(): ByteArray = ByteArray([email protected].
 }
 
 public actual fun isWindows(): Boolean = false
+
+internal actual fun identityHashCode(obj: Any?): Int = obj.identityHashCode()

packages/plugin-compiler/src/main/kotlin/io/realm/kotlin/compiler/RealmModelDefaultMethodGeneration.kt

@@ -0,0 +1,123 @@
+package io.realm.kotlin.compiler
+
+import org.jetbrains.kotlin.backend.common.extensions.IrPluginContext
+import org.jetbrains.kotlin.ir.builders.irGet
+import org.jetbrains.kotlin.ir.builders.irGetObject
+import org.jetbrains.kotlin.ir.builders.irReturn
+import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.IrProperty
+import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
+import org.jetbrains.kotlin.ir.expressions.impl.IrCallImpl
+import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.util.functions
+import org.jetbrains.kotlin.name.Name
+
+/**
+ * Class responsible for adding Realm specific logic to the default object methods like:
+ * - toString()
+ * - hashCode()
+ * - equals()
+ *
+ * WARNING: The current logic in here does not work well with incremental compilation. The reason
+ * is that we check if these methods are "empty" before filling them out, and during incremental
+ * compilation they already have content, and since all of these methods are using inlined
+ * methods they will not pick up changes in the RealmObjectHelper.
+ *
+ * This should only impact us as SDK developers though, but it does mean that changes to
+ * RealmObjectHelper methods will require a clean build to take effect.
+ */
+class RealmModelDefaultMethodGeneration(private val pluginContext: IrPluginContext) {
+
+    private val realmObjectHelper: IrClass = pluginContext.lookupClassOrThrow(FqNames.REALM_OBJECT_HELPER)
+    private val realmToString: IrSimpleFunction = realmObjectHelper.lookupFunction(Name.identifier("realmToString"))
+    private val realmEquals: IrSimpleFunction = realmObjectHelper.lookupFunction(Name.identifier("realmEquals"))
+    private val realmHashCode: IrSimpleFunction = realmObjectHelper.lookupFunction(Name.identifier("realmHashCode"))
+    private lateinit var objectReferenceProperty: IrProperty
+    private lateinit var objectReferenceType: IrType
+
+    fun addDefaultMethods(irClass: IrClass) {
+        objectReferenceProperty = irClass.lookupProperty(Names.OBJECT_REFERENCE)
+        objectReferenceType = objectReferenceProperty.backingField!!.type
+
+        if (syntheticMethodExists(irClass, "toString")) {
+            addToStringMethodBody(irClass)
+        }
+        if (syntheticMethodExists(irClass, "hashCode")) {
+            addHashCodeMethod(irClass)
+        }
+        if (syntheticMethodExists(irClass, "equals")) {
+            addEqualsMethod(irClass)
+        }
+    }
+
+    /**
+     * Checks if a synthetic method exists in the given class. Methods in super classes
+     * are ignored, only methods actually declared in the class will return `true`.
+     *
+     * These methods are created by an earlier step by the Realm compiler plugin and are
+     * recognized by not being fake and having an empty body.ß
+     */
+    private fun syntheticMethodExists(irClass: IrClass, methodName: String): Boolean {
+        return irClass.functions.firstOrNull {
+            !it.isFakeOverride && it.body == null && it.name == Name.identifier(methodName)
+        } != null
+    }
+
+    private fun addEqualsMethod(irClass: IrClass) {
+        val function: IrSimpleFunction = irClass.symbol.owner.functions.single { it.name.toString() == "equals" }
+        function.body = pluginContext.blockBody(function.symbol) {
+            +irReturn(
+                IrCallImpl(
+                    startOffset = startOffset,
+                    endOffset = endOffset,
+                    type = pluginContext.irBuiltIns.booleanType,
+                    symbol = realmEquals.symbol,
+                    typeArgumentsCount = 0,
+                    valueArgumentsCount = 2
+                ).apply {
+                    dispatchReceiver = irGetObject(realmObjectHelper.symbol)
+                    putValueArgument(0, irGet(function.dispatchReceiverParameter!!.type, function.dispatchReceiverParameter!!.symbol))
+                    putValueArgument(1, irGet(function.valueParameters[0].type, function.valueParameters[0].symbol))
+                }
+            )
+        }
+    }
+
+    private fun addHashCodeMethod(irClass: IrClass) {
+        val function: IrSimpleFunction = irClass.symbol.owner.functions.single { it.name.toString() == "hashCode" }
+        function.body = pluginContext.blockBody(function.symbol) {
+            +irReturn(
+                IrCallImpl(
+                    startOffset = startOffset,
+                    endOffset = endOffset,
+                    type = pluginContext.irBuiltIns.intType,
+                    symbol = realmHashCode.symbol,
+                    typeArgumentsCount = 0,
+                    valueArgumentsCount = 1
+                ).apply {
+                    dispatchReceiver = irGetObject(realmObjectHelper.symbol)
+                    putValueArgument(0, irGet(function.dispatchReceiverParameter!!.type, function.dispatchReceiverParameter!!.symbol))
+                }
+            )
+        }
+    }
+
+    private fun addToStringMethodBody(irClass: IrClass) {
+        val function: IrSimpleFunction = irClass.symbol.owner.functions.single { it.name.toString() == "toString" }
+        function.body = pluginContext.blockBody(function.symbol) {
+            +irReturn(
+                IrCallImpl(
+                    startOffset = startOffset,
+                    endOffset = endOffset,
+                    type = pluginContext.irBuiltIns.stringType,
+                    symbol = realmToString.symbol,
+                    typeArgumentsCount = 0,
+                    valueArgumentsCount = 1
+                ).apply {
+                    dispatchReceiver = irGetObject(realmObjectHelper.symbol)
+                    putValueArgument(0, irGet(function.dispatchReceiverParameter!!.type, function.dispatchReceiverParameter!!.symbol))
+                }
+            )
+        }
+    }
+}

packages/plugin-compiler/src/main/kotlin/io/realm/kotlin/compiler/RealmModelLoweringExtension.kt

@@ -107,6 +107,10 @@ private class RealmModelLowering(private val pluginContext: IrPluginContext) : C
             // Modify properties accessor to generate custom getter/setter
             AccessorModifierIrGeneration(pluginContext).modifyPropertiesAndCollectSchema(irClass)
 
+            // Add custom toString, equals and hashCode methods
+            val methodGenerator = RealmModelDefaultMethodGeneration(pluginContext)
+            methodGenerator.addDefaultMethods(irClass)
+
             // Add body for synthetic companion methods
             val companion = irClass.companionObject() ?: fatalError("RealmObject without companion: ${irClass.kotlinFqName}")
             generator.addCompanionFields(irClass, companion, SchemaCollector.properties[irClass])