IModelConnection
The frontend of an app does not open an iModel directly. Instead, it "connects" to an IModelDb that is managed by a backend through an
IModelConnection. IModelConnection is an abstract class that encapsulates the IModelDb on the frontend.
Various subclasses of IModelConnection are used depending on the type of connection:
CheckpointConnection is used to create a readonly connection to a Checkpoint of an iModel. A CheckpointConnection is initiated via CheckpointConnection.openRemote.
If the current process is a browser frontend, the connection will be to a remote backend using RPC. In that case, due to the nature of RPC requests, the backend servicing this connection may be servicing many simultaneous frontends, and may even change over time.
If the current process is connected to a private backend over IPC (e.g. on a desktop via Electron), the connection will be to an IModelDb of a Checkpoint from that private backend.
The primary difference between a CheckpointConnection using RPC vs. IPC is the lifetime of the IModelDb on the backend. For RPC, only the first client causes the IModelDb to be opened, and CheckpointConnection.close is ignored (because there can be more than one client). For IPC, every call to CheckpointConnection.openRemote attempts to open the IModelDb and CheckpointConnection.close closes it.
Obviously (because Checkpoints are immutable) CheckpointConnections only allow readonly access.
A SnapshotConnection can be used for readonly connections to a Snapshot iModel. It uses IPC, so may only be used from native applications.
A BriefcaseConnection may be used to connect to an editable BriefcaseDb. A BriefcaseConnection connects to a dedicated backend through Ipc. That means to create a BriefcaseConnection, the backend must have an active IpcHost and the frontend must have an active IpcApp. This will be true for NativeApps, the various MobileApps, and WebEditApps.
You can create a BlankConnection to show Views from sources other than an iModel.
Last Updated: 06 November, 2024