Updated the README example with acquire connection (#99)

* Updated the README example with acquire connection

Initially from reading the docs and examples I tried to use `&mut pool` instead of `&mut conn`. The compiler gave me an error that `Pool<MySql>` didn't implement `Executor`. I had to do a bit of digging and eventually just viewed the source of `Pool` to find `acquire()`, `try_acquire()` etc.

I think this change makes it a bit easier for someone to get started.

* Update README.md to reference initial pool declaration

* Fixed compile issues and added examples of using &mut &pool

README.md

@@ -88,8 +88,7 @@ sqlx = { version = "0.2", default-features = false, features = [ "runtime-tokio"
 
 #### Connect
 
-It is a very good idea to always create a connection pool at the beginning of your application
-and then share that.
+It is a very good idea to always create a connection pool at the beginning of your application and then share that.
 
 ```rust
 // Postgres
@@ -104,7 +103,7 @@ The result is an implementation of the `Row` trait. Values can be efficiently ac
 ```rust
 let row = sqlx::query("SELECT is_active FROM users WHERE id = ?")
     .bind(some_user_id)
-    .fetch_one(&mut conn)
+    .fetch_one(&mut &pool)
     .await?;
     
 let is_active: bool = row.get("is_active");
@@ -120,7 +119,7 @@ let countries = sqlx::query!(
         "SELECT country, COUNT(*) FROM users GROUP BY country WHERE organization = ?", 
         organization
     )
-    .fetch(&mut conn) // -> impl Stream<Item = { country: String, count: i64 }>
+    .fetch(&mut &pool) // -> impl Stream<Item = { country: String, count: i64 }>
     .map_ok(|rec| (rec.country, rec.count))
     .try_collect::<HashMap<_>>() // -> HashMap<String, i64>
     .await?;

examples/todos-postgres/src/main.rs

@@ -22,7 +22,7 @@ async fn main(args: Args) -> anyhow::Result<()> {
     match args.cmd {
         Some(Command::Add { description }) => {
             println!("Adding new todo with description '{}'", &description);
-            let todo_id = add_todo(&pool, &description).await?;
+            let todo_id = add_todo(&pool, description).await?;
             println!("Added new todo with id {}", todo_id);
         }
         Some(Command::Done { id }) => {
@@ -42,51 +42,43 @@ async fn main(args: Args) -> anyhow::Result<()> {
     Ok(())
 }
 
-async fn add_todo(pool: &PgPool, description: &str) -> anyhow::Result<i64> {
-    let mut tx = pool.begin().await?;
-
+async fn add_todo(mut pool: &PgPool, description: String) -> anyhow::Result<i64> {
     let rec = sqlx::query!(
-        "
+        r#"
 INSERT INTO todos ( description )
 VALUES ( $1 )
 RETURNING id
-        ",
+        "#,
         description
     )
-    .fetch_one(&mut tx)
+    .fetch_one(&mut pool)
     .await?;
 
-    tx.commit().await?;
-
     Ok(rec.id)
 }
 
-async fn complete_todo(pool: &PgPool, id: i64) -> anyhow::Result<bool> {
-    let mut tx = pool.begin().await?;
-
+async fn complete_todo(mut pool: &PgPool, id: i64) -> anyhow::Result<bool> {
     let rows_affected = sqlx::query!(
-        "
+        r#"
 UPDATE todos
 SET done = TRUE
 WHERE id = $1
-        ",
+        "#,
         id
     )
-    .execute(&mut tx)
+    .execute(&mut pool)
     .await?;
 
-    tx.commit().await?;
-
     Ok(rows_affected > 0)
 }
 
 async fn list_todos(pool: &mut PgPool) -> anyhow::Result<()> {
     let recs = sqlx::query!(
-        "
+        r#"
 SELECT id, description, done
 FROM todos
 ORDER BY id
-        "
+        "#
     )
     .fetch_all(pool)
     .await?;