fix diesel example (#460)

database_interactions/diesel/Cargo.toml

@@ -14,7 +14,6 @@ dotenv = "0.15"
 env_logger = "0.8"
 failure = "0.1.8"
 futures = "0.3.1"
-r2d2 = "0.8"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 uuid = { version = "0.8", features = ["serde", "v4"] }

database_interactions/diesel/src/actions.rs

@@ -3,11 +3,13 @@ use uuid::Uuid;
 
 use crate::models;
 
+type DbError = Box<dyn std::error::Error + Send + Sync>;
+
 /// Run query using Diesel to find user by uid and return it.
 pub fn find_user_by_uid(
     uid: Uuid,
     conn: &SqliteConnection,
-) -> Result<Option<models::User>, diesel::result::Error> {
+) -> Result<Option<models::User>, DbError> {
     use crate::schema::users::dsl::*;
 
     let user = users
@@ -23,7 +25,7 @@ pub fn insert_new_user(
     // prevent collision with `name` column imported inside the function
     nm: &str,
     conn: &SqliteConnection,
-) -> Result<models::User, diesel::result::Error> {
+) -> Result<models::User, DbError> {
     // It is common when using Diesel with Actix web to import schema-related
     // modules inside a function's scope (rather than the normal module's scope)
     // to prevent import collisions and namespace pollution.

database_interactions/diesel/src/main.rs

@@ -24,10 +24,12 @@ async fn get_user(
     user_uid: web::Path<Uuid>,
 ) -> Result<HttpResponse, Error> {
     let user_uid = user_uid.into_inner();
-    let conn = pool.get().expect("couldn't get db connection from pool");
 
     // use web::block to offload blocking Diesel code without blocking server thread
-    let user = web::block(move || actions::find_user_by_uid(user_uid, &conn))
+    let user = web::block(move || {
+        let conn = pool.get()?;
+        actions::find_user_by_uid(user_uid, &conn)
+    })
     .await
     .map_err(|e| {
         eprintln!("{}", e);
@@ -49,10 +51,11 @@ async fn add_user(
     pool: web::Data<DbPool>,
     form: web::Json<models::NewUser>,
 ) -> Result<HttpResponse, Error> {
-    let conn = pool.get().expect("couldn't get db connection from pool");
-
     // use web::block to offload blocking Diesel code without blocking server thread
-    let user = web::block(move || actions::insert_new_user(&form.name, &conn))
+    let user = web::block(move || {
+        let conn = pool.get()?;
+        actions::insert_new_user(&form.name, &conn)
+    })
     .await
     .map_err(|e| {
         eprintln!("{}", e);