Remove SqliteConnection#execute_pragma

We prefer to avoid polluting the main diesel crate with code that is
only needed for CLI or codegen. Unifying this code will aid with the
addition of prepared statement caching. All we really needed was the
ability to execute a SqlLiteral node directly.

Author: sgrif

diesel/src/expression/sql_literal.rs

@@ -35,6 +35,10 @@ impl<ST, DB> QueryFragment<DB> for SqlLiteral<ST> where
     }
 }
 
+impl<ST> Query for SqlLiteral<ST> {
+    type SqlType = ST;
+}
+
 impl<QS, ST> SelectableExpression<QS> for SqlLiteral<ST> {
 }
 

diesel/src/sqlite/connection/mod.rs

@@ -137,16 +137,6 @@ impl SqliteConnection {
         }
         query.map(|_| ())
     }
-
-    #[doc(hidden)]
-    pub fn execute_pragma<ST, U>(&self, source: &str) -> QueryResult<Vec<U>> where
-        U: Queryable<ST, Sqlite>,
-        <SqliteConnection as Connection>::Backend: HasSqlType<ST>,
-    {
-        Statement::prepare(&self.raw_connection, source)
-            .map(StatementIterator::new)
-            .and_then(Iterator::collect)
-    }
 }
 
 fn error_message(err_code: libc::c_int) -> &'static str {

diesel_codegen/src/schema_inference/sqlite.rs

@@ -1,4 +1,5 @@
 use diesel::*;
+use diesel::expression::dsl::sql;
 use diesel::sqlite::{SqliteConnection, Sqlite};
 use diesel::types::{HasSqlType, FromSqlRow};
 use syntax::ast;
@@ -22,8 +23,8 @@ table!{
 pub fn get_table_data(conn: &SqliteConnection, table_name: &str)
     -> QueryResult<Vec<ColumnInformation>>
 {
-    conn.execute_pragma::<pragma_table_info::SqlType, ColumnInformation>(
-        &format!("PRAGMA TABLE_INFO('{}')", table_name))
+    let query = format!("PRAGMA TABLE_INFO('{}')", table_name);
+    sql::<pragma_table_info::SqlType>(&query).load(conn)
 }
 
 fn is_text(type_name: &str) -> bool {
@@ -92,9 +93,10 @@ impl<ST> Queryable<ST, Sqlite> for FullTableInfo where
 }
 
 pub fn get_primary_keys(conn: &SqliteConnection, table_name: &str) -> QueryResult<Vec<String>> {
-    conn.execute_pragma::<pragma_table_info::SqlType, FullTableInfo>(
-        &format!("PRAGMA TABLE_INFO('{}')", table_name))
-        .map( |i| i.iter()
-               .filter_map(|i| if i.primary_key { Some(i.name.clone()) } else { None })
-               .collect())
+    let query = format!("PRAGMA TABLE_INFO('{}')", table_name);
+    let results = try!(sql::<pragma_table_info::SqlType>(&query)
+        .load::<FullTableInfo>(conn));
+    Ok(results.iter()
+        .filter_map(|i| if i.primary_key { Some(i.name.clone()) } else { None })
+        .collect())
 }