fraiseql_db/postgres/adapter/
relay.rs

1//! `RelayDatabaseAdapter` implementation for `PostgresAdapter`.
2
3use fraiseql_error::{FraiseQLError, Result};
4
5use super::{PostgresAdapter, escape_jsonb_key};
6use crate::{
7    dialect::PostgresDialect,
8    identifier::quote_postgres_identifier,
9    postgres::where_generator::PostgresWhereGenerator,
10    traits::{CursorValue, RelayDatabaseAdapter, RelayPageResult},
11    types::{
12        QueryParam,
13        sql_hints::{OrderByClause, OrderDirection},
14    },
15    where_clause::WhereClause,
16};
17
18impl RelayDatabaseAdapter for PostgresAdapter {
19    /// Execute keyset (cursor-based) pagination against a JSONB view.
20    ///
21    /// # `totalCount` semantics
22    ///
23    /// When `include_total_count` is `true`, **two queries** are issued on the same
24    /// connection:
25    ///
26    /// 1. A count query — `SELECT COUNT(*) FROM {view} WHERE {user_filter}` — that reflects the
27    ///    **full connection** size, ignoring cursor position. This is required by the Relay Cursor
28    ///    Connections spec, which defines `totalCount` as the count of all objects in the
29    ///    connection, regardless of `after`/`before`.
30    ///
31    /// 2. A page query — the cursor-filtered, limited result set.
32    ///
33    /// The two-query approach fixes a previous bug where `COUNT(*) OVER()` ran
34    /// inside the cursor-filtered subquery, causing `totalCount` to shrink as the
35    /// cursor advanced.  It also handles the edge case where the current page is
36    /// empty but the total count is non-zero (e.g., cursor past the last row).
37    ///
38    /// When `include_total_count` is `false`, only the page query is issued.
39    ///
40    /// # Performance note
41    ///
42    /// The count query scans all rows matching the user filter without LIMIT. On
43    /// large unfiltered tables this may be slow. Mitigations:
44    /// - Only enable `totalCount` when the client explicitly requests it (enforced by the executor
45    ///   via `include_total_count`).
46    /// - Add a `statement_timeout` on the connection for relay queries on very large datasets.
47    /// - Maintain a denormalised count table or materialised view for hot paths.
48    async fn execute_relay_page(
49        &self,
50        view: &str,
51        cursor_column: &str,
52        after: Option<CursorValue>,
53        before: Option<CursorValue>,
54        limit: u32,
55        forward: bool,
56        where_clause: Option<&WhereClause>,
57        order_by: Option<&[OrderByClause]>,
58        include_total_count: bool,
59    ) -> Result<RelayPageResult> {
60        let quoted_view = quote_postgres_identifier(view);
61        let quoted_col = quote_postgres_identifier(cursor_column);
62
63        // ── Cursor condition (page query only, NOT the count query) ────────────
64        //
65        // Per the Relay spec, totalCount ignores cursor position. The cursor
66        // condition is therefore excluded from the count query.
67        //
68        // The cursor occupies at most one parameter slot ($1) at the front of the
69        // page query's parameter list.
70        //
71        // UUID cursors use `$1::uuid` cast; BIGINT cursors use plain `$1`.
72        let cursor_param: Option<QueryParam>;
73        let cursor_where_part: Option<String>;
74        let active_cursor = if forward { after } else { before };
75        match active_cursor {
76            None => {
77                cursor_param = None;
78                cursor_where_part = None;
79            },
80            Some(CursorValue::Int64(pk)) => {
81                let op = if forward { ">" } else { "<" };
82                cursor_param = Some(QueryParam::BigInt(pk));
83                cursor_where_part = Some(format!("{quoted_col} {op} $1"));
84            },
85            Some(CursorValue::Uuid(uuid)) => {
86                let op = if forward { ">" } else { "<" };
87                cursor_param = Some(QueryParam::Text(uuid));
88                cursor_where_part = Some(format!("{quoted_col} {op} $1::uuid"));
89            },
90        }
91        let cursor_param_count: usize = usize::from(cursor_param.is_some());
92
93        // ── User WHERE clause ──────────────────────────────────────────────────
94        //
95        // Used in BOTH the count query (offset 0) and the page query (offset by
96        // cursor_param_count so parameter indices don't collide).
97        let mut user_where_json_params: Vec<serde_json::Value> = Vec::new();
98        let page_user_where_sql: Option<String> = if let Some(clause) = where_clause {
99            let generator = PostgresWhereGenerator::new(PostgresDialect);
100            let (sql, params) = generator.generate_with_param_offset(clause, cursor_param_count)?;
101            user_where_json_params = params;
102            Some(sql)
103        } else {
104            None
105        };
106        let user_param_count = user_where_json_params.len();
107
108        // ── ORDER BY clause ────────────────────────────────────────────────────
109        //
110        // Custom sort columns first, then cursor column as tiebreaker for stable
111        // keyset pagination.
112        let order_sql = if let Some(clauses) = order_by {
113            let mut parts: Vec<String> = clauses
114                .iter()
115                .map(|c| {
116                    let dir = match c.direction {
117                        OrderDirection::Asc => "ASC",
118                        OrderDirection::Desc => "DESC",
119                    };
120                    // escape_jsonb_key is defense-in-depth: field names are already
121                    // validated as GraphQL identifiers (which cannot contain `'`).
122                    format!("data->>'{field}' {dir}", field = escape_jsonb_key(&c.field))
123                })
124                .collect();
125            let primary_dir = if forward { "ASC" } else { "DESC" };
126            parts.push(format!("{quoted_col} {primary_dir}"));
127            format!(" ORDER BY {}", parts.join(", "))
128        } else {
129            let dir = if forward { "ASC" } else { "DESC" };
130            format!(" ORDER BY {quoted_col} {dir}")
131        };
132
133        // ── Page WHERE SQL ─────────────────────────────────────────────────────
134        //
135        // Combines cursor condition AND user filter with offset parameter indices.
136        let cursor_part = cursor_where_part.as_deref().unwrap_or("");
137        let user_part =
138            page_user_where_sql.as_deref().map(|s| format!("({s})")).unwrap_or_default();
139        let page_where_sql = if cursor_part.is_empty() && user_part.is_empty() {
140            String::new()
141        } else if cursor_part.is_empty() {
142            format!(" WHERE {user_part}")
143        } else if user_part.is_empty() {
144            format!(" WHERE {cursor_part}")
145        } else {
146            format!(" WHERE {cursor_part} AND {user_part}")
147        };
148
149        // ── LIMIT parameter index ──────────────────────────────────────────────
150        let limit_idx = cursor_param_count + user_param_count + 1;
151
152        // ── Page SQL ───────────────────────────────────────────────────────────
153        //
154        // Backward pagination wraps the inner query in a subquery to re-sort
155        // the descending page back to ascending order.
156        let page_sql = if forward {
157            format!("SELECT data FROM {quoted_view}{page_where_sql}{order_sql} LIMIT ${limit_idx}")
158        } else {
159            let inner = format!(
160                "SELECT data, {quoted_col} AS _relay_cursor \
161                 FROM {quoted_view}{page_where_sql}{order_sql} LIMIT ${limit_idx}"
162            );
163            format!("SELECT data FROM ({inner}) _relay_page ORDER BY _relay_cursor ASC")
164        };
165
166        // ── Page params: [cursor?, user_where_params..., limit] ────────────────
167        let mut page_typed_params: Vec<QueryParam> = Vec::new();
168        if let Some(cp) = cursor_param {
169            page_typed_params.push(cp);
170        }
171        for v in &user_where_json_params {
172            page_typed_params.push(QueryParam::from(v.clone()));
173        }
174        page_typed_params.push(QueryParam::BigInt(i64::from(limit)));
175
176        let client = self.acquire_connection_with_retry().await?;
177
178        // ── Execute page query ─────────────────────────────────────────────────
179        let page_param_refs: Vec<&(dyn tokio_postgres::types::ToSql + Sync)> = page_typed_params
180            .iter()
181            .map(|p| p as &(dyn tokio_postgres::types::ToSql + Sync))
182            .collect();
183
184        let page_rows = client.query(&page_sql, &page_param_refs).await.map_err(|e| {
185            FraiseQLError::Database {
186                message:   e.to_string(),
187                sql_state: e.code().map(|c| c.code().to_string()),
188            }
189        })?;
190
191        let rows: Vec<crate::types::JsonbValue> = page_rows
192            .iter()
193            .map(|row| {
194                let data: serde_json::Value = row.get("data");
195                crate::types::JsonbValue::new(data)
196            })
197            .collect();
198
199        // ── Count query (Relay spec: totalCount ignores cursor position) ────────
200        //
201        // The WHERE clause is regenerated with offset 0 (no cursor parameter prefix)
202        // because this is a standalone query. Using the same connection avoids an
203        // extra pool acquisition.
204        let total_count = if include_total_count {
205            let (count_sql, count_typed_params) = if let Some(clause) = where_clause {
206                let generator = PostgresWhereGenerator::new(PostgresDialect);
207                let (where_sql, params) = generator.generate_with_param_offset(clause, 0)?;
208                let sql = format!("SELECT COUNT(*) FROM {quoted_view} WHERE ({where_sql})");
209                let typed: Vec<QueryParam> = params.into_iter().map(QueryParam::from).collect();
210                (sql, typed)
211            } else {
212                (format!("SELECT COUNT(*) FROM {quoted_view}"), Vec::<QueryParam>::new())
213            };
214
215            let count_param_refs: Vec<&(dyn tokio_postgres::types::ToSql + Sync)> =
216                count_typed_params
217                    .iter()
218                    .map(|p| p as &(dyn tokio_postgres::types::ToSql + Sync))
219                    .collect();
220
221            let count_row = client.query_one(&count_sql, &count_param_refs).await.map_err(|e| {
222                FraiseQLError::Database {
223                    message:   e.to_string(),
224                    sql_state: e.code().map(|c| c.code().to_string()),
225                }
226            })?;
227
228            let total: i64 = count_row.get(0);
229            // cast_unsigned() is the clippy-recommended alternative to `as u64` for i64;
230            // it has the same bit-pattern semantics but makes the sign-loss intent explicit.
231            // Row counts from COUNT(*) are always non-negative so sign loss is impossible.
232            Some(total.cast_unsigned())
233        } else {
234            None
235        };
236
237        Ok(RelayPageResult { rows, total_count })
238    }
239}
fraiseql_db/postgres/adapter/relay.rs

fraiseql_db/postgres/adapter/
relay.rs
