Paginator API (#10)

* Paginator

* Remove unnecessary dependency, rename to num_pages

* Hotfix - nullable json value

* num_pages implemented on sub_query

Cargo.toml

@@ -32,6 +32,8 @@ serde = { version = "^1.0", features = [ "derive" ] }
 sqlx = { version = "^0.5", optional = true }
 strum = { version = "^0.20", features = [ "derive" ] }
 serde_json = { version = "^1", optional = true }
+async-stream = { version = "^0.3" }
+futures-util = { version = "^0.3" }
 
 [features]
 debug-print = []

examples/sqlx-mysql/Cargo.toml

@@ -10,3 +10,6 @@ sea-orm = { path = "../../", features = [ "sqlx-mysql", "runtime-async-std-nativ
 # sea-query = { path = "../../../sea-query" }
 strum = { version = "^0.20", features = [ "derive" ] }
 serde_json = { version = "^1" }
+futures = { version = "^0.3" }
+async-stream = { version = "^0.3" }
+futures-util = { version = "^0.3" }

examples/sqlx-mysql/src/select.rs

@@ -26,6 +26,18 @@ pub async fn all_about_select(db: &Database) -> Result<(), QueryErr> {
         all_about_select_json(db).await?;
     }
 
+    println!("===== =====\n");
+
+    find_all_stream(&db).await.unwrap();
+
+    println!("===== =====\n");
+
+    find_first_page(&db).await.unwrap();
+
+    println!("===== =====\n");
+
+    find_num_pages(&db).await.unwrap();
+
     Ok(())
 }
 
@@ -232,3 +244,66 @@ async fn count_fruits_by_cake_json(db: &Database) -> Result<(), QueryErr> {
 
     Ok(())
 }
+
+async fn find_all_stream(db: &Database) -> Result<(), QueryErr> {
+    use futures::TryStreamExt;
+    use std::time::Duration;
+    use async_std::task::sleep;
+
+    println!("find all cakes: ");
+    let mut cake_paginator = cake::Entity::find().paginate(db, 2);
+    while let Some(cake_res) = cake_paginator.fetch_and_next().await? {
+        for cake in cake_res {
+            println!("{:?}", cake);
+        }
+    }
+
+    println!();
+    println!("find all fruits: ");
+    let mut fruit_paginator = fruit::Entity::find().paginate(db, 2);
+    while let Some(fruit_res) = fruit_paginator.fetch_and_next().await? {
+        for fruit in fruit_res {
+            println!("{:?}", fruit);
+        }
+    }
+
+    println!();
+    println!("find all fruits with stream: ");
+    let mut fruit_stream = fruit::Entity::find().paginate(db, 2).into_stream();
+    while let Some(fruits) = fruit_stream.try_next().await? {
+        for fruit in fruits {
+            println!("{:?}", fruit);
+        }
+        sleep(Duration::from_millis(250)).await;
+    }
+
+    println!();
+    println!("find all fruits in json with stream: ");
+    let mut json_stream = fruit::Entity::find().into_json().paginate(db, 2).into_stream();
+    while let Some(jsons) = json_stream.try_next().await? {
+        for json in jsons {
+            println!("{:?}", json);
+        }
+        sleep(Duration::from_millis(250)).await;
+    }
+
+    Ok(())
+}
+
+async fn find_first_page(db: &Database) -> Result<(), QueryErr> {
+    println!("fruits first page: ");
+    let page = fruit::Entity::find().paginate(db, 2).fetch_page(0).await?;
+    for fruit in page {
+        println!("{:?}", fruit);
+    }
+
+    Ok(())
+}
+
+async fn find_num_pages(db: &Database) -> Result<(), QueryErr> {
+    println!("fruits number of page: ");
+    let num_pages = fruit::Entity::find().paginate(db, 2).num_pages().await?;
+    println!("{:?}", num_pages);
+
+    Ok(())
+}

src/connector/mod.rs

@@ -1,10 +1,12 @@
 mod executor;
 mod insert;
+mod paginator;
 mod select;
 mod update;
 
 pub use executor::*;
 pub use insert::*;
+pub use paginator::*;
 pub use select::*;
 pub use update::*;
 

src/connector/paginator.rs

@@ -0,0 +1,87 @@
+use crate::{Connection, Database, QueryErr, SelectorTrait};
+use futures::Stream;
+use async_stream::stream;
+use std::{marker::PhantomData, pin::Pin};
+use sea_query::{Alias, Expr, SelectStatement};
+
+pub type PinBoxStream<'db, Item> = Pin<Box<dyn Stream<Item = Item> + 'db>>;
+
+#[derive(Clone, Debug)]
+pub struct Paginator<'db, S>
+where
+    S: SelectorTrait + 'db,
+{
+    pub(crate) query: SelectStatement,
+    pub(crate) page: usize,
+    pub(crate) page_size: usize,
+    pub(crate) db: &'db Database,
+    pub(crate) selector: PhantomData<S>,
+}
+
+impl<'db, S> Paginator<'db, S>
+where
+    S: SelectorTrait + 'db,
+{
+    pub async fn fetch_page(&mut self, page: usize) -> Result<Vec<S::Item>, QueryErr> {
+        self.query.limit(self.page_size as u64).offset((self.page_size * page) as u64);
+        let builder = self.db.get_query_builder_backend();
+        let stmt = self.query.build(builder).into();
+        let rows = self.db.get_connection().query_all(stmt).await?;
+        let mut buffer = Vec::with_capacity(rows.len());
+        for row in rows.into_iter() {
+            // TODO: Error handling
+            buffer.push(S::from_raw_query_result(row).map_err(|_e| QueryErr)?);
+        }
+        Ok(buffer)
+    }
+
+    pub async fn fetch(&mut self) -> Result<Vec<S::Item>, QueryErr> {
+        self.fetch_page(self.page).await
+    }
+
+    pub async fn num_pages(&mut self) -> Result<usize, QueryErr> {
+        let builder = self.db.get_query_builder_backend();
+        let stmt = SelectStatement::new()
+            .expr(Expr::cust("COUNT(*) AS num_rows"))
+            .from_subquery(
+                self.query.clone().reset_limit().reset_offset().to_owned(),
+                Alias::new("sub_query")
+            )
+            .build(builder)
+            .into();
+        let result = match self.db.get_connection().query_one(stmt).await? {
+            Some(res) => res,
+            None => return Ok(0),
+        };
+        let num_rows = result.try_get::<i32>("", "num_rows").map_err(|_e| QueryErr)? as usize;
+        let num_pages = (num_rows / self.page_size) + (num_rows % self.page_size > 0) as usize;
+        Ok(num_pages)
+    }
+
+    pub fn next(&mut self) {
+        self.page += 1;
+    }
+
+    pub async fn fetch_and_next(&mut self) -> Result<Option<Vec<S::Item>>, QueryErr> {
+        let vec = self.fetch().await?;
+        self.next();
+        let opt = if !vec.is_empty() {
+            Some(vec)
+        } else {
+            None
+        };
+        Ok(opt)
+    }
+
+    pub fn into_stream(mut self) -> PinBoxStream<'db, Result<Vec<S::Item>, QueryErr>> {
+        Box::pin(stream! {
+            loop {
+                if let Some(vec) = self.fetch_and_next().await? {
+                    yield Ok(vec);
+                } else {
+                    break
+                }
+            }
+        })
+    }
+}

src/connector/select.rs

@@ -1,7 +1,4 @@
-use crate::{
-    query::combine, Connection, Database, EntityTrait, FromQueryResult, JsonValue, QueryErr,
-    QueryResult, Select, SelectTwo, Statement, TypeErr,
-};
+use crate::{Connection, Database, EntityTrait, FromQueryResult, JsonValue, Paginator, QueryErr, QueryResult, Select, SelectTwo, Statement, TypeErr, query::combine};
 use sea_query::{QueryBuilder, SelectStatement};
 use std::marker::PhantomData;
 
@@ -91,6 +88,10 @@ where
     pub async fn all(self, db: &Database) -> Result<Vec<E::Model>, QueryErr> {
         self.into_model::<E::Model>().all(db).await
     }
+
+    pub fn paginate<'db>(self, db: &'db Database, page_size: usize) -> Paginator<'db, SelectModel<E::Model>> {
+        self.into_model::<E::Model>().paginate(db, page_size)
+    }
 }
 
 impl<E, F> SelectTwo<E, F>
@@ -156,4 +157,14 @@ where
         }
         Ok(models)
     }
+
+    pub fn paginate<'db>(self, db: &'db Database, page_size: usize) -> Paginator<'db, S> {
+        Paginator {
+            query: self.query,
+            page: 0,
+            page_size,
+            db,
+            selector: PhantomData,
+        }
+    }
 }

src/query/json.rs

@@ -18,7 +18,7 @@ impl FromQueryResult for JsonValue {
                     macro_rules! match_mysql_type {
                         ( $type: ty ) => {
                             if <$type as Type<MySql>>::type_info().eq(col_type) {
-                                map.insert(col.to_owned(), json!(res.try_get::<$type>(pre, &col)?));
+                                map.insert(col.to_owned(), json!(res.try_get::<Option<$type>>(pre, &col)?));
                                 continue;
                             }
                         };