Add Kotlin serialization-based APIs

common/main/java/com/couchbase/lite/Document.java

@@ -622,6 +622,13 @@ private void setC4Document(@Nullable C4Document c4doc, boolean mutable) {
         }
     }
 
+    // for use by CollectionExtensions.kt
+    void setContent(@NonNull FLDict data, boolean mutable) {
+        synchronized (lock) {
+            setContentLocked(data, mutable);
+        }
+    }
+
     @GuardedBy("lock")
     private void updateC4DocumentLocked(@Nullable C4Document c4Doc) {
         if (c4Document == c4Doc) { return; }

common/main/java/com/couchbase/lite/Result.java

@@ -523,13 +523,27 @@ public String toJSON() throws CouchbaseLiteException {
     public Iterator<String> iterator() { return getKeys().iterator(); }
 
     //---------------------------------------------
-    // private access
+    // package access -- for use by QueryExtensions.kt
     //---------------------------------------------
 
-    private int getColumnCount() { return context.getResultSet().getColumnCount(); }
+    @NonNull
+    List<FLValue> getFLValues() { return values; }
 
     @NonNull
-    private List<String> getColumnNames() { return context.getResultSet().getColumnNames(); }
+    List<String> getColumnNames() { return context.getResultSet().getColumnNames(); }
+
+    int getIndexForKey(String key) {
+        final int index = context.getResultSet().getColumnIndex(Preconditions.assertNotNull(key, "key"));
+        if (index < 0) { return -1; }
+        if ((missingColumns & (1L << index)) != 0) { return -1; }
+        return (!isInBounds(index)) ? -1 : index;
+    }
+
+    //---------------------------------------------
+    // private access
+    //---------------------------------------------
+
+    private int getColumnCount() { return context.getResultSet().getColumnCount(); }
 
     @Nullable
     private Object getFleeceAt(int index) {
@@ -546,13 +560,6 @@ private FLValue getFLValueAt(int index) {
         return values.get(index);
     }
 
-    private int getIndexForKey(@Nullable String key) {
-        final int index = context.getResultSet().getColumnIndex(Preconditions.assertNotNull(key, "key"));
-        if (index < 0) { return -1; }
-        if ((missingColumns & (1L << index)) != 0) { return -1; }
-        return (!isInBounds(index)) ? -1 : index;
-    }
-
     @NonNull
     private List<FLValue> extractColumns(@NonNull FLArrayIterator columns) {
         final int n = getColumnCount();

common/main/java/com/couchbase/lite/internal/fleece/FLValue.java

@@ -325,6 +325,6 @@ public Object toJava() {
     <T> T withContent(@NonNull Fn.NonNullFunction<Long, T> fn) { return fn.apply(peer); }
 
     @NonNull
-    FLArray asFLArray() { return FLArray.create(impl.nAsArray(peer)); }
+    public FLArray asFLArray() { return FLArray.create(impl.nAsArray(peer)); }
 }
 

common/main/kotlin/com/couchbase/lite/CollectionExtensions.kt

@@ -0,0 +1,153 @@
+//
+// Copyright (c) 2026 Couchbase, Inc All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+@file:OptIn(ExperimentalSerializationApi::class)
+
+package com.couchbase.lite
+
+import com.couchbase.lite.internal.core.C4Document
+import com.couchbase.lite.internal.fleece.*
+import kotlinx.serialization.*
+
+
+/** Document model classes must implement this interface.
+ *  It adds a [documentMeta] property that's used by Couchbase Lite. */
+interface DocumentModel {
+    /** This tags the model instance with the document ID and revision it was read from,
+     *  which enables conflict detection when it's later saved.
+     *  You may read this property, but DO NOT alter it.
+     *  It should be implemented as a stored property defaulting to `null`, for example:
+     *  `@Transient override var documentMeta: DocumentMeta? = null` */
+    @Transient var documentMeta: DocumentMeta?
+}
+
+/** Stores the Couchbase Lite metadata of a document. Used by the [DocumentModel] interface. */
+class DocumentMeta internal constructor(val collection: Collection?, // [Result] leaves it null
+                                        val id: String,
+                                        val revisionID: String)
+
+
+/** Gets an existing document with the given ID, and uses Kotlin Serialization to create an
+ *  instance of class [T] from it. [T] must implement [DocumentModel].
+ *  If a document with the given ID doesn't exist in the collection, returns null. */
+@ExperimentalSerializationApi
+inline fun <reified T: DocumentModel> Collection.getDocumentAs(id: String): T? =
+    getDocumentAs(id, serializer())
+
+@ExperimentalSerializationApi
+fun <T: DocumentModel> Collection.getDocumentAs(id: String, deserializer: DeserializationStrategy<T>): T? =
+    modelFromC4Doc(this, id, getC4Document(id), deserializer)
+
+
+/**
+ * Saves a [DocumentModel] instance as a document in the collection, with a specified conflict handler.
+ * If the model's [DocumentModel.documentMeta] property is null, it will be saved as a new document with the
+ * given [docID], which must not be null.
+ * Otherwise the [DocumentModel.documentMeta] property determines the document ID and prior revision ID, and the
+ * [docID] parameter should be null.
+ * After a successful save, the [DocumentModel.documentMeta] property is updated to the current state. */
+@ExperimentalSerializationApi
+inline fun <reified T: DocumentModel> Collection.save(model: T,
+                                                      docID: String? = null,
+                                                      noinline conflictHandler: ModelConflictHandler<T>? = null) =
+    save(model, serializer(), serializer(), docID, conflictHandler)
+
+@ExperimentalSerializationApi
+fun <T: DocumentModel> Collection.save(model: T,
+                                       serializer: SerializationStrategy<T>,
+                                       deserializer: DeserializationStrategy<T>,
+                                       docID: String? = null,
+                                       conflictHandler: ModelConflictHandler<T>? = null): Boolean
+{
+    // Get or create the Document:
+    val meta = model.documentMeta
+    val doc: MutableDocument
+    if (meta == null) {
+        require(docID != null) { "docID argument must be given when saving a new document" }
+        doc = MutableDocument(docID)
+    } else {
+        require(meta.collection == this || meta.collection == null) {"saving document to wrong collection"}
+        require(docID == null || docID == meta.id) {"docID parameter does not match meta.id"}
+        doc = getDocument(meta.id)?.toMutable() ?: MutableDocument(meta.id)
+    }
+
+    // Subroutine that calls the ModelConflictHandler & updates the model accordingly:
+    fun handleConflict(doc: MutableDocument?, curDoc: Document?): Boolean {
+        val curModel = curDoc?.let {modelFromC4Doc(this, it.id, it.c4doc, deserializer)}
+        val ok = conflictHandler!!(model, curModel)
+        if (ok)
+            doc?.setContentFromModel(model, serializer)
+        return ok
+    }
+
+    if (doc.revisionID != meta?.revisionID) {
+        // Model is out of date -- have to resolve the conflict
+        if (!handleConflict(null, doc))
+            return false
+    }
+
+    // Replace the document's content with the serialized model:
+    if (doc.collection == null) {
+        doc.collection = this
+    }
+    doc.setContentFromModel(model, serializer)
+
+    // Save:
+    val ok = if (conflictHandler != null) {
+        save(doc) {savingDoc, curDoc -> handleConflict(savingDoc, curDoc) }
+    } else {
+        save(doc)
+        true
+    }
+    if (ok)
+        model.documentMeta = DocumentMeta(this, doc.id, doc.revisionID!!)
+    return ok
+}
+
+
+/** Model-based conflict handler callback, used by [Collection.save] with [DocumentModel] objects.
+ *  The first parameter is the [DocumentModel] you are saving.
+ *  The second parameter is a [DocumentModel] deserialized from the conflicting revision in the collection,
+ *  or null if the document has been deleted.
+ *
+ *  The function may modify the first [DocumentModel] -- the one being saved -- to incorporate changes from
+ *  the other [DocumentModel] (the revision in the database), then return true. (But it should NOT modify
+ *  its [DocumentModel.documentMeta] property.)
+ *
+ *  Or it may return false to signal that it can't handle the conflict. */
+typealias ModelConflictHandler<T> = (T, T?)-> Boolean
+
+
+/** Creates a [DocumentModel] instance from a [C4Document]. */
+private fun <T:DocumentModel> modelFromC4Doc(collection: Collection,
+                                             docID: String,
+                                             c4doc: C4Document?,
+                                             deserializer: DeserializationStrategy<T>): T?
+{
+    if (c4doc == null || c4doc.isDocDeleted) return null
+    val properties = c4doc.selectedBody2 ?: return null
+    val model = deserializeFromFleece(properties.toFLValue(), deserializer)
+    model.documentMeta = DocumentMeta(collection, docID, c4doc.revID!!)
+    return model
+}
+
+
+/** Extension of [MutableDocument], that updates its content from a [DocumentModel] object. */
+private fun <T:DocumentModel> MutableDocument.setContentFromModel(model: T, serializer: SerializationStrategy<T>) {
+    val body = serializeToFleece(serializer, model)
+    val root = FLValue.fromData(body).asFLDict()
+    setContent(root, false)
+}

common/main/kotlin/com/couchbase/lite/QueryExtensions.kt

@@ -0,0 +1,129 @@
+//
+// Copyright (c) 2026 Couchbase, Inc All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+package com.couchbase.lite
+
+import com.couchbase.lite.internal.fleece.*
+import kotlinx.serialization.DeserializationStrategy
+import kotlinx.serialization.ExperimentalSerializationApi
+import kotlinx.serialization.descriptors.StructureKind
+import kotlinx.serialization.serializer
+
+
+/** Uses Kotlin Serialization to create an object of type [T] from the query row.
+ *  If the [key] parameter is non-null, it uses the row's value for that key as the source,
+ *  instead of the entire row.
+ *
+ *  For example, if your query is `SELECT name, age, shoeSize FROM people` and you have a
+ *  serializable Person class with properties name, age and shoeSize, you can call:
+ *  `val person = result.data<Person>()`
+ *
+ *  Or you could use the query `SELECT * as person FROM people` and create the Person with
+ *  `val person = result.data<Person>("person")`.
+ *  */
+@ExperimentalSerializationApi
+inline fun <reified T> Result.data(key: String? = null): T =
+    data(serializer(), key)
+
+/** Uses Kotlin Serialization to create a [DocumentModel] instance of type [T] from the query row.
+ *  This is a specialization of the one-parameter [data] method that adds a [metaKey] parameter.
+ *
+ *  The [metaKey] parameter is the name of the result property whose value comes from the N1QL
+ *  `meta()` function; this is used to set the [DocumentModel.documentMeta] property of the result.
+ *
+ *  For example, if your query is `SELECT * as person, meta() as meta FROM people`, you would call
+ *  `result.data<Person>("person", "meta")`.
+ */
+@ExperimentalSerializationApi
+inline fun <reified T: DocumentModel> Result.data(key: String? = null,
+                                                  metaKey: String? = null): T =
+    data(serializer(), key, metaKey)
+
+@ExperimentalSerializationApi
+fun <T> Result.data(deserializer: DeserializationStrategy<T>,
+                    key: String? = null,
+                    metaKey: String? = null): T
+{
+    val columns = flValues
+    val result = if (key == null) {
+        if (deserializer.descriptor as? StructureKind == StructureKind.LIST) {
+            // Deserializer wants a List, so pass the column values directly:
+            deserializeFromFleece(columns, deserializer)
+        } else {
+            // Deserializer wants a Map, so smush the column names and values together:
+            val size = columns.size
+            val names = columnNames
+            val iter = object: Iterator<Map.Entry<String,FLValue>> {
+                var i = 0
+                override fun hasNext() = i < size
+                override fun next(): Map.Entry<String,FLValue> {
+                    val entry = Entry(names[i], columns[i])
+                    i++
+                    return entry
+                }
+            }
+            deserializeFromFleece(iter, size, deserializer)
+        }
+    } else {
+        // Deserializing a single value from the result:
+        val i = getIndexForKey(key)
+        if (i < 0) throw CouchbaseLiteError("Query row has no property '$key'")
+        deserializeFromFleece(columns[i], deserializer)
+    }
+    if (result is DocumentModel && metaKey != null)
+        result.documentMeta = getDocumentMeta(metaKey)
+    return result
+}
+
+
+/** Returns the query rows transformed by Kotlin Serialization into instances of [T]. */
+@ExperimentalSerializationApi
+inline fun <reified T> ResultSet.data(key: String? = null): Sequence<T> =
+    data(serializer(), key)
+
+@ExperimentalSerializationApi
+inline fun <reified T: DocumentModel> ResultSet.data(key: String? = null,
+                                                     metaKey: String? = null): Sequence<T> =
+    data(serializer(), key, metaKey)
+
+/** Returns the query rows transformed by Kotlin Serialization into instances of [T]. */
+@ExperimentalSerializationApi
+fun <T> ResultSet.data(deserializer: DeserializationStrategy<T>,
+                       key: String? = null,
+                       metaKey: String? = null): Sequence<T> =
+    sequence {
+        while (true) {
+            val result = next() ?: break
+            yield(result.data(deserializer, key, metaKey))
+        }
+    }
+
+
+// A trivial implementation of [Map.Entry].
+private class Entry(override val key: String, override val value: FLValue) : Map.Entry<String,FLValue>
+
+
+// Creates a [DocumentMeta] from the "meta" column of a Result. (Note: It can't set the `collection`.)
+private fun Result.getDocumentMeta(key: String): DocumentMeta? {
+    val i = getIndexForKey(key)
+    if (i < 0) throw CouchbaseLiteError("Query row has no property '$key'")
+    val col = flValues[i]
+    if (col.type != FLValue.DICT) return null
+    val meta = col.asFLDict()
+    val id = meta["id"]?.asString() ?: return null
+    val revID = meta["revisionID"]?.asString() ?: return null
+    return DocumentMeta(null, id, revID)
+}