Add custom error type to database module

src/backend/database/error.rs

@@ -0,0 +1,26 @@
+use thiserror::Error;
+
+/// Error that happens within the database module.
+#[derive(Error, Debug)]
+pub enum DatabaseError {
+    #[error(transparent)]
+    ConnectionError(#[from] diesel::result::ConnectionError),
+
+    #[error(transparent)]
+    MigrationsError(#[from] diesel_migrations::RunMigrationsError),
+
+    #[error(transparent)]
+    QueryError(#[from] diesel::result::Error),
+
+    #[error(transparent)]
+    SendError(#[from] std::sync::mpsc::SendError<super::thread::Action>),
+
+    #[error(transparent)]
+    ReceiveError(#[from] futures_channel::oneshot::Canceled),
+
+    #[error("Database error: {0}")]
+    Other(String),
+}
+
+/// Return type for database methods.
+pub type DatabaseResult<T> = Result<T, DatabaseError>;