Merge pull request diesel-rs#2799 from weiznich/feature/load_returns_a_iterator

Return a iterator from `Connection::load`

Author: weiznich

diesel/Cargo.toml

@@ -16,7 +16,7 @@ edition = "2018"
 byteorder = "1.0"
 chrono = { version = "0.4.19", optional = true, default-features = false, features = ["clock", "std"] }
 libc = { version = "0.2.0", optional = true }
-libsqlite3-sys = { version = ">=0.8.0, <0.23.0", optional = true, features = ["min_sqlite_version_3_7_16"] }
+libsqlite3-sys = { version = ">=0.8.0, <0.23.0", optional = true, features = ["bundled_bindings"] }
 mysqlclient-sys = { version = "0.2.0", optional = true }
 pq-sys = { version = "0.4.0", optional = true }
 quickcheck = { version = "0.9.0", optional = true }
@@ -44,7 +44,7 @@ ipnetwork = ">=0.12.2, <0.19.0"
 quickcheck = "0.9"
 
 [features]
-default = ["with-deprecated", "32-column-tables"]
+default = ["32-column-tables", "with-deprecated"]
 extras = ["chrono", "serde_json", "uuid", "network-address", "numeric", "r2d2"]
 unstable = ["diesel_derives/nightly"]
 large-tables = ["32-column-tables"]

diesel/src/connection/mod.rs

@@ -6,14 +6,12 @@ mod transaction_manager;
 use std::fmt::Debug;
 
 use crate::backend::Backend;
-use crate::deserialize::FromSqlRow;
 use crate::expression::QueryMetadata;
 use crate::query_builder::{AsQuery, QueryFragment, QueryId};
-use crate::query_dsl::load_dsl::CompatibleType;
 use crate::result::*;
 
 #[doc(hidden)]
-pub use self::statement_cache::{MaybeCached, StatementCache, StatementCacheKey};
+pub use self::statement_cache::{MaybeCached, PrepareForCache, StatementCache, StatementCacheKey};
 pub use self::transaction_manager::{AnsiTransactionManager, TransactionManager};
 
 /// Perform simple operations on a backend.
@@ -27,8 +25,25 @@ pub trait SimpleConnection {
     fn batch_execute(&mut self, query: &str) -> QueryResult<()>;
 }
 
+/// This trait describes which cursor type is used by a given connection
+/// implementation. This trait is only useful in combination with [`Connection`].
+///
+/// Implementation wise this is a workaround for GAT's
+pub trait ConnectionGatWorkaround<'a, DB: Backend> {
+    /// The cursor type returned by [`Connection::load`]
+    ///
+    /// Users should handle this as opaque type that implements [`Iterator`]
+    type Cursor: Iterator<Item = QueryResult<Self::Row>>;
+    /// The row type used as [`Iterator::Item`] for the iterator implementation
+    /// of [`ConnectionGatWorkaround::Cursor`]
+    type Row: crate::row::Row<'a, DB>;
+}
+
 /// A connection to a database
-pub trait Connection: SimpleConnection + Sized + Send {
+pub trait Connection: SimpleConnection + Sized + Send
+where
+    Self: for<'a> ConnectionGatWorkaround<'a, <Self as Connection>::Backend>,
+{
     /// The backend this type connects to
     type Backend: Backend;
 
@@ -177,12 +192,13 @@ pub trait Connection: SimpleConnection + Sized + Send {
     fn execute(&mut self, query: &str) -> QueryResult<usize>;
 
     #[doc(hidden)]
-    fn load<T, U, ST>(&mut self, source: T) -> QueryResult<Vec<U>>
+    fn load<T>(
+        &mut self,
+        source: T,
+    ) -> QueryResult<<Self as ConnectionGatWorkaround<Self::Backend>>::Cursor>
     where
         T: AsQuery,
         T::Query: QueryFragment<Self::Backend> + QueryId,
-        T::SqlType: CompatibleType<U, Self::Backend, SqlType = ST>,
-        U: FromSqlRow<ST, Self::Backend>,
         Self::Backend: QueryMetadata<T::SqlType>;
 
     #[doc(hidden)]

diesel/src/connection/statement_cache.rs

@@ -107,6 +107,12 @@ pub struct StatementCache<DB: Backend, Statement> {
     pub cache: HashMap<StatementCacheKey<DB>, Statement>,
 }
 
+#[derive(Debug, Clone, Copy)]
+pub enum PrepareForCache {
+    Yes,
+    No,
+}
+
 #[allow(clippy::len_without_is_empty, clippy::new_without_default)]
 impl<DB, Statement> StatementCache<DB, Statement>
 where
@@ -133,23 +139,23 @@ where
     ) -> QueryResult<MaybeCached<Statement>>
     where
         T: QueryFragment<DB> + QueryId,
-        F: FnOnce(&str) -> QueryResult<Statement>,
+        F: FnOnce(&str, PrepareForCache) -> QueryResult<Statement>,
     {
         use std::collections::hash_map::Entry::{Occupied, Vacant};
 
         let cache_key = StatementCacheKey::for_source(source, bind_types)?;
 
         if !source.is_safe_to_cache_prepared()? {
             let sql = cache_key.sql(source)?;
-            return prepare_fn(&sql).map(MaybeCached::CannotCache);
+            return prepare_fn(&sql, PrepareForCache::No).map(MaybeCached::CannotCache);
         }
 
         let cached_result = match self.cache.entry(cache_key) {
             Occupied(entry) => entry.into_mut(),
             Vacant(entry) => {
                 let statement = {
                     let sql = entry.key().sql(source)?;
-                    prepare_fn(&sql)
+                    prepare_fn(&sql, PrepareForCache::Yes)
                 };
 
                 entry.insert(statement?)

diesel/src/mysql/connection/bind.rs

@@ -11,11 +11,23 @@ use crate::mysql::types::MYSQL_TIME;
 use crate::mysql::{MysqlType, MysqlValue};
 use crate::result::QueryResult;
 
-pub struct Binds {
+pub struct PreparedStatementBinds(Binds);
+
+pub struct OutputBinds(Binds);
+
+impl Clone for OutputBinds {
+    fn clone(&self) -> Self {
+        Self(Binds {
+            data: self.0.data.clone(),
+        })
+    }
+}
+
+struct Binds {
     data: Vec<BindData>,
 }
 
-impl Binds {
+impl PreparedStatementBinds {
     pub fn from_input_data<Iter>(input: Iter) -> QueryResult<Self>
     where
         Iter: IntoIterator<Item = (MysqlType, Option<Vec<u8>>)>,
@@ -25,34 +37,31 @@ impl Binds {
             .map(BindData::for_input)
             .collect::<Vec<_>>();
 
-        Ok(Binds { data })
+        Ok(Self(Binds { data }))
     }
 
-    pub fn from_output_types(types: Vec<Option<MysqlType>>, metadata: &StatementMetadata) -> Self {
+    pub fn with_mysql_binds<F, T>(&mut self, f: F) -> T
+    where
+        F: FnOnce(*mut ffi::MYSQL_BIND) -> T,
+    {
+        self.0.with_mysql_binds(f)
+    }
+}
+
+impl OutputBinds {
+    pub fn from_output_types(types: &[Option<MysqlType>], metadata: &StatementMetadata) -> Self {
         let data = metadata
             .fields()
             .iter()
-            .zip(types.into_iter().chain(std::iter::repeat(None)))
+            .zip(types.iter().copied().chain(std::iter::repeat(None)))
             .map(|(field, tpe)| BindData::for_output(tpe, field))
             .collect();
 
-        Binds { data }
-    }
-
-    pub fn with_mysql_binds<F, T>(&mut self, f: F) -> T
-    where
-        F: FnOnce(*mut ffi::MYSQL_BIND) -> T,
-    {
-        let mut binds = self
-            .data
-            .iter_mut()
-            .map(|x| unsafe { x.mysql_bind() })
-            .collect::<Vec<_>>();
-        f(binds.as_mut_ptr())
+        Self(Binds { data })
     }
 
     pub fn populate_dynamic_buffers(&mut self, stmt: &Statement) -> QueryResult<()> {
-        for (i, data) in self.data.iter_mut().enumerate() {
+        for (i, data) in self.0.data.iter_mut().enumerate() {
             data.did_numeric_overflow_occur()?;
             // This is safe because we are re-binding the invalidated buffers
             // at the end of this function
@@ -69,20 +78,37 @@ impl Binds {
     }
 
     pub fn update_buffer_lengths(&mut self) {
-        for data in &mut self.data {
+        for data in &mut self.0.data {
             data.update_buffer_length();
         }
     }
 
-    pub fn len(&self) -> usize {
-        self.data.len()
+    pub fn with_mysql_binds<F, T>(&mut self, f: F) -> T
+    where
+        F: FnOnce(*mut ffi::MYSQL_BIND) -> T,
+    {
+        self.0.with_mysql_binds(f)
+    }
+}
+
+impl Binds {
+    fn with_mysql_binds<F, T>(&mut self, f: F) -> T
+    where
+        F: FnOnce(*mut ffi::MYSQL_BIND) -> T,
+    {
+        let mut binds = self
+            .data
+            .iter_mut()
+            .map(|x| unsafe { x.mysql_bind() })
+            .collect::<Vec<_>>();
+        f(binds.as_mut_ptr())
     }
 }
 
-impl Index<usize> for Binds {
+impl Index<usize> for OutputBinds {
     type Output = BindData;
     fn index(&self, index: usize) -> &Self::Output {
-        &self.data[index]
+        &self.0.data[index]
     }
 }
 
@@ -122,7 +148,7 @@ impl From<u32> for Flags {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct BindData {
     tpe: ffi::enum_field_types,
     bytes: Vec<u8>,
@@ -713,9 +739,8 @@ mod tests {
             )
             .unwrap();
 
-        let mut stmt = conn
-            .prepare_query(&crate::sql_query(
-                "SELECT
+        let mut stmt = conn.prepared_query(&crate::sql_query(
+            "SELECT
                     tiny_int, small_int, medium_int, int_col,
                     big_int, unsigned_int, zero_fill_int,
                     numeric_col, decimal_col, float_col, double_col, bit_col,
@@ -725,30 +750,21 @@ mod tests {
                     ST_AsText(polygon_col), ST_AsText(multipoint_col), ST_AsText(multilinestring_col),
                     ST_AsText(multipolygon_col), ST_AsText(geometry_collection), json_col
                  FROM all_mysql_types",
-            ))
-            .unwrap();
+        )).unwrap();
 
         let metadata = stmt.metadata().unwrap();
         let mut output_binds =
-            Binds::from_output_types(vec![None; metadata.fields().len()], &metadata);
+            OutputBinds::from_output_types(&vec![None; metadata.fields().len()], &metadata);
         stmt.execute_statement(&mut output_binds).unwrap();
         stmt.populate_row_buffers(&mut output_binds).unwrap();
 
         let results: Vec<(BindData, &_)> = output_binds
+            .0
             .data
             .into_iter()
             .zip(metadata.fields())
             .collect::<Vec<_>>();
 
-        macro_rules! matches {
-            ($expression:expr, $( $pattern:pat )|+ $( if $guard: expr )?) => {
-                match $expression {
-                    $( $pattern )|+ $( if $guard )? => true,
-                    _ => false
-                }
-            }
-        }
-
         let tiny_int_col = &results[0].0;
         assert_eq!(tiny_int_col.tpe, ffi::enum_field_types::MYSQL_TYPE_TINY);
         assert!(tiny_int_col.flags.contains(Flags::NUM_FLAG));
@@ -1057,9 +1073,9 @@ mod tests {
         assert!(!polygon_col.flags.contains(Flags::ENUM_FLAG));
         assert!(!polygon_col.flags.contains(Flags::BINARY_FLAG));
         assert_eq!(
-            to_value::<Text, String>(polygon_col).unwrap(),
-            "MULTIPOLYGON(((28 26,28 0,84 0,84 42,28 26),(52 18,66 23,73 9,48 6,52 18)),((59 18,67 18,67 13,59 13,59 18)))"
-        );
+                to_value::<Text, String>(polygon_col).unwrap(),
+                "MULTIPOLYGON(((28 26,28 0,84 0,84 42,28 26),(52 18,66 23,73 9,48 6,52 18)),((59 18,67 18,67 13,59 13,59 18)))"
+            );
 
         let geometry_collection = &results[32].0;
         assert_eq!(
@@ -1105,12 +1121,12 @@ mod tests {
 
         let bind = BindData::for_test_output(bind_tpe.into());
 
-        let mut binds = Binds { data: vec![bind] };
+        let mut binds = OutputBinds(Binds { data: vec![bind] });
 
         stmt.execute_statement(&mut binds).unwrap();
         stmt.populate_row_buffers(&mut binds).unwrap();
 
-        binds.data.remove(0)
+        binds.0.data.remove(0)
     }
 
     fn input_bind(
@@ -1144,9 +1160,9 @@ mod tests {
             is_truncated: None,
         };
 
-        let binds = Binds {
+        let binds = PreparedStatementBinds(Binds {
             data: vec![id_bind, field_bind],
-        };
+        });
         stmt.input_bind(binds).unwrap();
         stmt.did_an_error_occur().unwrap();
         unsafe {