App: Do not update the db if its empty

If the source table is empty skipp the database refresh.

podcasts-data/src/dbqueries.rs

@@ -392,7 +392,7 @@ pub fn is_episodes_populated() -> Result<bool, DataError> {
 
 /// Check if the `shows` table contains any rows
 ///
-/// Return true if `shows table is populated.
+/// Return true if `shows` table is populated.
 pub fn is_podcasts_populated(filter_ids: &[i32]) -> Result<bool, DataError> {
     use schema::shows::dsl::*;
 
@@ -404,6 +404,20 @@ pub fn is_podcasts_populated(filter_ids: &[i32]) -> Result<bool, DataError> {
         .map_err(From::from)
 }
 
+/// Check if the `source` table contains any rows
+///
+/// Return true if `source` table is populated.
+pub fn is_source_populated(filter_ids: &[i32]) -> Result<bool, DataError> {
+    use schema::source::dsl::*;
+
+    let db = connection();
+    let con = db.get()?;
+
+    select(exists(source.filter(id.ne_all(filter_ids))))
+        .get_result(&con)
+        .map_err(From::from)
+}
+
 pub(crate) fn index_new_episodes(eps: &[NewEpisode]) -> Result<(), DataError> {
     use schema::episodes::dsl::*;
     let db = connection();