(DOCSP-26735): C++: Add a Quick Start page (#2575)

## Pull Request Info

As part of this work, I removed the "LINQ" reference in the include that
was shared across all the SDKs, and replaced it with the more generic
"the SDK's query engine."

### Jira

- https://jira.mongodb.org/browse/DOCSP-26735

### Staged Changes

- [Quick
Start](https://docs-mongodbcom-staging.corp.mongodb.com/realm/docsworker-xlarge/DOCSP-26735/sdk/cpp/quick-start/)
- [App
Services](https://docs-mongodbcom-staging.corp.mongodb.com/realm/docsworker-xlarge/DOCSP-26735/sdk/cpp/application-services/)

### Reminder Checklist

If your PR modifies the docs, you might need to also update some
corresponding
pages. Check if completed or N/A.

- [x] Create Jira ticket for corresponding docs-app-services update(s),
if any
- [x] Checked/updated Admin API
- [x] Checked/updated CLI reference

### Review Guidelines


[REVIEWING.md](https://github.com/mongodb/docs-realm/blob/master/REVIEWING.md)

examples/cpp/CMakeLists.txt

@@ -19,8 +19,15 @@ FetchContent_Declare(
 
 FetchContent_MakeAvailable(Catch2 cpprealm)
 
-# add_executable(examples testHelpers.hpp testHelpersTests.cpp authentication.cpp define-object-model.cpp examples.cpp flexible-sync.cpp supported-types.cpp)
-add_executable(examples authentication.cpp define-object-model.cpp examples.cpp filter-data.cpp flexible-sync.cpp supported-types.cpp)
+add_executable(examples 
+  authentication.cpp 
+  define-object-model.cpp 
+  examples.cpp 
+  filter-data.cpp 
+  flexible-sync.cpp 
+  quick-start.cpp 
+  supported-types.cpp
+)
 
 target_link_libraries(examples PRIVATE Catch2::Catch2WithMain)
 target_link_libraries(examples PRIVATE cpprealm)

examples/cpp/quick-start.cpp

@@ -0,0 +1,169 @@
+#include <catch2/catch_test_macros.hpp>
+#include <thread>
+#include <future>
+#include <string>
+// :snippet-start: includes
+#include <cpprealm/sdk.hpp>
+// :snippet-end:
+
+// :replace-start: {
+//   "terms": {
+//     "Local_": "",
+//     "Sync_": "",
+//     "userId.c_str()": "userId"
+//   }
+// }
+
+static const std::string APP_ID = "cpp-tester-uliix";
+
+struct Local_Todo : realm::object<Local_Todo> {
+    realm::persisted<std::string> name;
+    realm::persisted<std::string> status;
+
+    static constexpr auto schema = realm::schema("Local_Todo",
+        realm::property<&Local_Todo::name>("name"),
+        realm::property<&Local_Todo::status>("status"));
+};
+
+// :snippet-start: model
+struct Sync_Todo : realm::object<Sync_Todo> {
+    realm::persisted<realm::object_id> _id{realm::object_id::generate()};
+    realm::persisted<std::string> name;
+    realm::persisted<std::string> status;
+    // The ownerId property stores the user.identifier() of a
+    // logged-in user. Omit this property for the non-sync example.
+    realm::persisted<std::string> ownerId;
+
+    static constexpr auto schema = realm::schema("Sync_Todo",
+        realm::property<&Sync_Todo::_id, true>("_id"),
+        realm::property<&Sync_Todo::name>("name"),
+        realm::property<&Sync_Todo::status>("status"),
+        realm::property<&Sync_Todo::ownerId>("ownerId"));
+};
+// :snippet-end:
+
+TEST_CASE("local quick start", "[realm][write]") {
+    // :snippet-start: realm-open
+    auto realm = realm::open<Local_Todo>();
+    // :snippet-end:
+
+    // :snippet-start: create-todo
+    auto todo = Local_Todo {
+        .name = "Create my first todo item",
+        .status = "In Progress"
+    };
+
+    realm.write([&realm, &todo] {
+        realm.add(todo);
+    });
+    // :snippet-end:
+
+    // :snippet-start: get-all-todos
+    auto todos = realm.objects<Local_Todo>();
+    // :snippet-end:
+    CHECK(todos.size() == 1);
+
+    // :snippet-start: filter
+    auto todosInProgress = todos.where([](auto const& todo) {
+        return todo.status == "In Progress";
+    });
+    // :snippet-end:
+    CHECK(todosInProgress.size() == 1);
+
+    // :snippet-start: watch-for-changes
+    auto token = todo.observe([&](auto&& change) {
+        try {
+            if (change.error) {
+                rethrow_exception(change.error);
+            }
+            if (change.is_deleted) {
+                std::cout << "The object was deleted.\n";
+            } else {
+                for (auto& propertyChange : change.property_changes) {
+                    std::cout << "The object's " << propertyChange.name << " property has changed.\n";
+                    CHECK(propertyChange.name == "status"); // :remove:
+                }
+            }
+        } catch (std::exception const& e) {
+            std::cerr << "Error: " << e.what() << "\n";
+        }
+    });
+    // :snippet-end:
+
+    // :snippet-start: modify-write-block
+    auto todoToUpdate = todosInProgress[0];
+    realm.write([&realm, &todoToUpdate] {
+        todoToUpdate.status = "Complete";
+    });
+    // :snippet-end:
+    CHECK(*todoToUpdate.status == "Complete");
+
+    // :snippet-start: delete
+    realm.write([&realm, &todo] {
+        realm.remove(todo);
+    });
+    // :snippet-end:
+}
+
+TEST_CASE("sync quick start", "[realm][write][sync]") {
+    // :snippet-start: connect-to-backend
+    auto app = realm::App(APP_ID);
+    // :snippet-end:
+
+    // :snippet-start: authenticate-user
+    auto user = app.login(realm::App::credentials::anonymous()).get_future().get();
+    // :snippet-end:
+
+    // :snippet-start: open-synced-realm
+    auto sync_config = user.flexible_sync_configuration();
+    auto synced_realm_ref = realm::async_open<Sync_Todo>(sync_config).get_future().get();
+    auto realm = synced_realm_ref.resolve();
+    // :remove-start:
+    // Remove any existing subscriptions before adding the one for this example
+    auto clearInitialSubscriptions = realm.subscriptions().update([](auto &subs) {
+        subs.clear();
+    }).get_future().get();
+    CHECK(clearInitialSubscriptions == true);
+    CHECK(realm.subscriptions().size() == 0);
+    // :remove-end:
+    // For this example, get the userId for the Flexible Sync query
+    auto userId = user.identifier();
+    auto subscriptions = realm.subscriptions();
+    auto updateSubscriptionSuccess = subscriptions.update([&](realm::mutable_sync_subscription_set &subs) {
+        subs.add<Sync_Todo>("todos", [&userId](auto &obj) {
+            // For this example, get only Sync_Todo items where the ownerId
+            // property value is equal to the userId of the logged-in user.
+            return obj.ownerId == userId;
+        });
+    }).get_future().get();
+    // :snippet-end:
+    CHECK(updateSubscriptionSuccess == true);
+
+    // The C++ SDK is currently missing a constructor to store a std::string
+    // So convert the userId std::string to a character array for persisting.
+    // TODO: Remove this and use the userId directly when the constructor is added.
+    // :snippet-start: write-to-synced-realm
+    auto todo = Sync_Todo {
+        .name = "Create a Sync todo item",
+        .status = "In Progress",
+        .ownerId = userId.c_str()
+    };
+
+    realm.write([&realm, &todo] {
+        realm.add(todo);
+    });
+
+    auto todos = realm.objects<Sync_Todo>();
+    // :snippet-end:
+    CHECK(todos.size() == 1);
+
+    // The C++ SDK does not yet expose `waitForUpload` and `waitForDownload`
+    // so add a delay to prevent the connection from terminating while syncing
+    sleep(5);
+    realm.write([&realm, &todo] {
+        realm.remove(todo);
+    });
+    sleep(5);
+}
+
+// :replace-end:

snooty.toml

@@ -14,6 +14,7 @@ toc_landing_pages = [
   # SDKs
   "/sdk",
   "/sdk/cpp",
+  "/sdk/cpp/application-services",
   "/sdk/cpp/manage-users",
   "/sdk/java",
   "/sdk/java/api",

source/examples/generated/cpp/quick-start.snippet.authenticate-user.cpp

@@ -0,0 +1 @@
+auto user = app.login(realm::App::credentials::anonymous()).get_future().get();

source/examples/generated/cpp/quick-start.snippet.connect-to-backend.cpp

@@ -0,0 +1 @@
+auto app = realm::App(APP_ID);

source/examples/generated/cpp/quick-start.snippet.create-todo.cpp

@@ -0,0 +1,8 @@
+auto todo = Todo {
+    .name = "Create my first todo item",
+    .status = "In Progress"
+};
+
+realm.write([&realm, &todo] {
+    realm.add(todo);
+});

source/examples/generated/cpp/quick-start.snippet.delete.cpp

@@ -0,0 +1,3 @@
+realm.write([&realm, &todo] {
+    realm.remove(todo);
+});

source/examples/generated/cpp/quick-start.snippet.filter.cpp

@@ -0,0 +1,3 @@
+auto todosInProgress = todos.where([](auto const& todo) {
+    return todo.status == "In Progress";
+});

source/examples/generated/cpp/quick-start.snippet.get-all-todos.cpp

@@ -0,0 +1 @@
+auto todos = realm.objects<Todo>();

source/examples/generated/cpp/quick-start.snippet.includes.cpp

@@ -0,0 +1 @@
+#include <cpprealm/sdk.hpp>

source/examples/generated/cpp/quick-start.snippet.model.cpp

@@ -0,0 +1,14 @@
+struct Todo : realm::object<Todo> {
+    realm::persisted<realm::object_id> _id{realm::object_id::generate()};
+    realm::persisted<std::string> name;
+    realm::persisted<std::string> status;
+    // The ownerId property stores the user.identifier() of a
+    // logged-in user. Omit this property for the non-sync example.
+    realm::persisted<std::string> ownerId;
+
+    static constexpr auto schema = realm::schema("Todo",
+        realm::property<&Todo::_id, true>("_id"),
+        realm::property<&Todo::name>("name"),
+        realm::property<&Todo::status>("status"),
+        realm::property<&Todo::ownerId>("ownerId"));
+};

source/examples/generated/cpp/quick-start.snippet.modify-write-block.cpp

@@ -0,0 +1,4 @@
+auto todoToUpdate = todosInProgress[0];
+realm.write([&realm, &todoToUpdate] {
+    todoToUpdate.status = "Complete";
+});

source/examples/generated/cpp/quick-start.snippet.open-synced-realm.cpp

@@ -0,0 +1,13 @@
+auto sync_config = user.flexible_sync_configuration();
+auto synced_realm_ref = realm::async_open<Todo>(sync_config).get_future().get();
+auto realm = synced_realm_ref.resolve();
+// For this example, get the userId for the Flexible Sync query
+auto userId = user.identifier();
+auto subscriptions = realm.subscriptions();
+auto updateSubscriptionSuccess = subscriptions.update([&](realm::mutable_sync_subscription_set &subs) {
+    subs.add<Todo>("todos", [&userId](auto &obj) {
+        // For this example, get only Todo items where the ownerId
+        // property value is equal to the userId of the logged-in user.
+        return obj.ownerId == userId;
+    });
+}).get_future().get();

source/examples/generated/cpp/quick-start.snippet.realm-open.cpp

@@ -0,0 +1 @@
+auto realm = realm::open<Todo>();

source/examples/generated/cpp/quick-start.snippet.watch-for-changes.cpp

@@ -0,0 +1,16 @@
+auto token = todo.observe([&](auto&& change) {
+    try {
+        if (change.error) {
+            rethrow_exception(change.error);
+        }
+        if (change.is_deleted) {
+            std::cout << "The object was deleted.\n";
+        } else {
+            for (auto& propertyChange : change.property_changes) {
+                std::cout << "The object's " << propertyChange.name << " property has changed.\n";
+            }
+        }
+    } catch (std::exception const& e) {
+        std::cerr << "Error: " << e.what() << "\n";
+    }
+});

source/examples/generated/cpp/quick-start.snippet.write-to-synced-realm.cpp

@@ -0,0 +1,11 @@
+auto todo = Todo {
+    .name = "Create a Sync todo item",
+    .status = "In Progress",
+    .ownerId = userId
+};
+
+realm.write([&realm, &todo] {
+    realm.add(todo);
+});
+
+auto todos = realm.objects<Todo>();

source/includes/note-unsupported-flex-sync-rql-operators.rst

@@ -1,5 +1,5 @@
 .. note::
 
    Flexible Sync does not support all the query operators available in Realm 
-   Query Language and LINQ. See :ref:`Flexible Sync RQL Limitations 
-   <flexible-sync-rql-limitations>` for details.
+   Query Language and the SDK's query engine. See :ref:`Flexible Sync RQL 
+   Limitations <flexible-sync-rql-limitations>` for details.

source/sdk/cpp.txt

@@ -9,14 +9,14 @@ C++ SDK (Alpha)
 
    Why Realm Database? </sdk/cpp/realm-database>
    Install Realm </sdk/cpp/install>
+   Quick Start </sdk/cpp/quick-start>
    Model Data </sdk/cpp/model-data>
    Configure & Open a Realm </sdk/cpp/realm-files/configure-and-open-a-realm>
    CRUD </sdk/cpp/crud/>
    React to Changes </sdk/cpp/react-to-changes>
-   Connect to App Services </sdk/cpp/app-services/connect-to-app>
+   Application Services </sdk/cpp/application-services>
    Manage Users </sdk/cpp/manage-users>
    Manage Sync Subscriptions </sdk/cpp/sync/sync-subscriptions>
-   Call an Atlas Function </sdk/cpp/app-services/call-a-function>
    GitHub <https://github.com/realm/realm-cpp>
    API Reference (Doxygen) <https://www.mongodb.com/docs/realm-sdks/cpp/latest/>