Split the storage trait from the implementation

crates/storage/src/pagination.rs

@@ -14,10 +14,8 @@
 
 //! Utilities to manage paginated queries.
 
-use sqlx::{Database, QueryBuilder};
 use thiserror::Error;
 use ulid::Ulid;
-use uuid::Uuid;
 
 /// An error returned when invalid pagination parameters are provided
 #[derive(Debug, Error)]
@@ -26,14 +24,14 @@ pub struct InvalidPagination;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct Pagination {
-    before: Option<Ulid>,
-    after: Option<Ulid>,
-    count: usize,
-    direction: PaginationDirection,
+    pub before: Option<Ulid>,
+    pub after: Option<Ulid>,
+    pub count: usize,
+    pub direction: PaginationDirection,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
-enum PaginationDirection {
+pub enum PaginationDirection {
     Forward,
     Backward,
 }
@@ -101,60 +99,8 @@ impl Pagination {
         self
     }
 
-    /// Add cursor-based pagination to a query, as used in paginated GraphQL
-    /// connections
-    fn generate_pagination<'a, DB>(&self, query: &mut QueryBuilder<'a, DB>, id_field: &'static str)
-    where
-        DB: Database,
-        Uuid: sqlx::Type<DB> + sqlx::Encode<'a, DB>,
-        i64: sqlx::Type<DB> + sqlx::Encode<'a, DB>,
-    {
-        // ref: https://github.com/graphql/graphql-relay-js/issues/94#issuecomment-232410564
-        // 1. Start from the greedy query: SELECT * FROM table
-
-        // 2. If the after argument is provided, add `id > parsed_cursor` to the `WHERE`
-        // clause
-        if let Some(after) = self.after {
-            query
-                .push(" AND ")
-                .push(id_field)
-                .push(" > ")
-                .push_bind(Uuid::from(after));
-        }
-
-        // 3. If the before argument is provided, add `id < parsed_cursor` to the
-        // `WHERE` clause
-        if let Some(before) = self.before {
-            query
-                .push(" AND ")
-                .push(id_field)
-                .push(" < ")
-                .push_bind(Uuid::from(before));
-        }
-
-        match self.direction {
-            // 4. If the first argument is provided, add `ORDER BY id ASC LIMIT first+1` to the
-            // query
-            PaginationDirection::Forward => {
-                query
-                    .push(" ORDER BY ")
-                    .push(id_field)
-                    .push(" ASC LIMIT ")
-                    .push_bind((self.count + 1) as i64);
-            }
-            // 5. If the first argument is provided, add `ORDER BY id DESC LIMIT last+1` to the
-            // query
-            PaginationDirection::Backward => {
-                query
-                    .push(" ORDER BY ")
-                    .push(id_field)
-                    .push(" DESC LIMIT ")
-                    .push_bind((self.count + 1) as i64);
-            }
-        };
-    }
-
     /// Process a page returned by a paginated query
+    #[must_use]
     pub fn process<T>(&self, mut edges: Vec<T>) -> Page<T> {
         let is_full = edges.len() == (self.count + 1);
         if is_full {
@@ -198,7 +144,6 @@ impl<T> Page<T> {
         }
     }
 
-    #[must_use]
     pub fn try_map<F, E, T2>(self, f: F) -> Result<Page<T2>, E>
     where
         F: FnMut(T) -> Result<T2, E>,
@@ -211,23 +156,3 @@ impl<T> Page<T> {
         })
     }
 }
-
-/// An extension trait to the `sqlx` [`QueryBuilder`], to help adding pagination
-/// to a query
-pub trait QueryBuilderExt {
-    /// Add cursor-based pagination to a query, as used in paginated GraphQL
-    /// connections
-    fn generate_pagination(&mut self, id_field: &'static str, pagination: Pagination) -> &mut Self;
-}
-
-impl<'a, DB> QueryBuilderExt for QueryBuilder<'a, DB>
-where
-    DB: Database,
-    Uuid: sqlx::Type<DB> + sqlx::Encode<'a, DB>,
-    i64: sqlx::Type<DB> + sqlx::Encode<'a, DB>,
-{
-    fn generate_pagination(&mut self, id_field: &'static str, pagination: Pagination) -> &mut Self {
-        pagination.generate_pagination(self, id_field);
-        self
-    }
-}