simplify retrieval in find_by_host()

we can use "first()" instead of limit(1).load().etc…
since on a UNIQUE field, we only expect 1 result.

first() returns QueryResult, which is Result<T, diesel::Error>, so we
need to implement a converter for that error type.

This commit addresses @fdb-hiroshima's review.

plume-models/src/blogs.rs

@@ -1,6 +1,6 @@
 use activitypub::{actor::Group, collection::OrderedCollection, object::Image, CustomObject};
 use chrono::NaiveDateTime;
-use diesel::{self, ExpressionMethods, QueryDsl, RunQueryDsl, SaveChangesDsl};
+use diesel::{self, ExpressionMethods, QueryDsl, QueryResult, RunQueryDsl, SaveChangesDsl};
 use openssl::{
     hash::MessageDigest,
     pkey::{PKey, Private},
@@ -195,14 +195,10 @@ impl Blog {
         }
     }
 
-    pub fn find_by_host(c: &PlumeRocket, host: Host) -> Result<Blog> {
-        let from_db = blogs::table
+    pub fn find_by_host(c: &PlumeRocket, host: Host) -> QueryResult<Blog> {
+        blogs::table
             .filter(blogs::custom_domain.eq(host))
-            .limit(1)
-            .load::<Blog>(&*c.conn)?
-            .into_iter()
-            .next();
-        from_db.ok_or(Error::NotFound)
+            .first::<Blog>(&*c.conn)
     }
 
     fn fetch_from_webfinger(c: &PlumeRocket, acct: &str) -> Result<Blog> {

src/routes/errors.rs

@@ -14,6 +14,12 @@ impl From<Error> for ErrorPage {
     }
 }
 
+impl From<diesel::result::Error> for ErrorPage {
+    fn from(err: diesel::result::Error) -> ErrorPage {
+        ErrorPage(plume_models::Error::Db(err))
+    }
+}
+
 impl<'r> Responder<'r> for ErrorPage {
     fn respond_to(self, req: &Request) -> response::Result<'r> {
         let rockets = req.guard::<PlumeRocket>().unwrap();