trezy.codes
forked from
slices.network/quickslice
Auto-indexing service and GraphQL API for AT Protocol Records
docs: add pagination placeholder fix plan
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
chadtmiller.com
+520
+520
dev-docs/plans/2026-01-19-fix-pagination-placeholders.md
+520
dev-docs/plans/2026-01-19-fix-pagination-placeholders.md
···
1
+
# Fix Pagination Cursor Placeholder Bug
2
+
3
+
> **For Claude:** REQUIRED SUB-SKILL: Use superpowers:executing-plans to implement this plan task-by-task.
4
+
5
+
**Goal:** Fix cursor-based pagination (`after`/`before`) which returns 0 results on PostgreSQL due to incorrect SQL placeholders.
6
+
7
+
**Architecture:** The `build_cursor_where_clause` function in `pagination.gleam` uses literal `?` placeholders, but PostgreSQL requires numbered placeholders (`$1`, `$2`, etc.). We need to pass the executor and a starting index so proper placeholders can be generated.
8
+
9
+
**Tech Stack:** Gleam, PostgreSQL, SQLite
10
+
11
+
---
12
+
13
+
## Root Cause
14
+
15
+
In `server/src/database/queries/pagination.gleam`, the `build_cursor_where_clause` and `build_progressive_clauses` functions build SQL with literal `?`:
16
+
17
+
```gleam
18
+
let new_part = field_ref <> " = ?" // Line 261
19
+
let comparison_part = field_ref <> " " <> comparison_op <> " ?" // Line 273
20
+
```
21
+
22
+
But PostgreSQL needs `$1, $2, $3`. The executor has a `placeholder(index)` function that returns the correct format for each dialect, but it's not being used.
23
+
24
+
---
25
+
26
+
### Task 1: Update `build_cursor_where_clause` Signature
27
+
28
+
**Files:**
29
+
- Modify: `server/src/database/queries/pagination.gleam:210-237`
30
+
31
+
**Step 1: Update function signature to accept start_index**
32
+
33
+
Change the function signature from:
34
+
35
+
```gleam
36
+
pub fn build_cursor_where_clause(
37
+
exec: Executor,
38
+
decoded_cursor: DecodedCursor,
39
+
sort_by: Option(List(#(String, String))),
40
+
is_before: Bool,
41
+
) -> #(String, List(String)) {
42
+
```
43
+
44
+
To:
45
+
46
+
```gleam
47
+
pub fn build_cursor_where_clause(
48
+
exec: Executor,
49
+
decoded_cursor: DecodedCursor,
50
+
sort_by: Option(List(#(String, String))),
51
+
is_before: Bool,
52
+
start_index: Int,
53
+
) -> #(String, List(String)) {
54
+
```
55
+
56
+
**Step 2: Update the call to build_progressive_clauses**
57
+
58
+
Change line 225-231 from:
59
+
60
+
```gleam
61
+
let clauses =
62
+
build_progressive_clauses(
63
+
exec,
64
+
sort_fields,
65
+
decoded_cursor.field_values,
66
+
decoded_cursor.cid,
67
+
is_before,
68
+
)
69
+
```
70
+
71
+
To:
72
+
73
+
```gleam
74
+
let clauses =
75
+
build_progressive_clauses(
76
+
exec,
77
+
sort_fields,
78
+
decoded_cursor.field_values,
79
+
decoded_cursor.cid,
80
+
is_before,
81
+
start_index,
82
+
)
83
+
```
84
+
85
+
**Step 3: Run build to check for compilation errors**
86
+
87
+
Run: `cd ~/code/quickslice/server && gleam build`
88
+
Expected: Compilation errors about missing argument (we'll fix callers in Task 3)
89
+
90
+
---
91
+
92
+
### Task 2: Update `build_progressive_clauses` to Use Numbered Placeholders
93
+
94
+
**Files:**
95
+
- Modify: `server/src/database/queries/pagination.gleam:239-307`
96
+
97
+
**Step 1: Update function signature**
98
+
99
+
Change line 240-246 from:
100
+
101
+
```gleam
102
+
fn build_progressive_clauses(
103
+
exec: Executor,
104
+
sort_fields: List(#(String, String)),
105
+
field_values: List(String),
106
+
cid: String,
107
+
is_before: Bool,
108
+
) -> #(List(String), List(String)) {
109
+
```
110
+
111
+
To:
112
+
113
+
```gleam
114
+
fn build_progressive_clauses(
115
+
exec: Executor,
116
+
sort_fields: List(#(String, String)),
117
+
field_values: List(String),
118
+
cid: String,
119
+
is_before: Bool,
120
+
start_index: Int,
121
+
) -> #(List(String), List(String)) {
122
+
```
123
+
124
+
**Step 2: Rewrite the function body to track placeholder indices**
125
+
126
+
Replace the entire function body (lines 247-307) with:
127
+
128
+
```gleam
129
+
fn build_progressive_clauses(
130
+
exec: Executor,
131
+
sort_fields: List(#(String, String)),
132
+
field_values: List(String),
133
+
cid: String,
134
+
is_before: Bool,
135
+
start_index: Int,
136
+
) -> #(List(String), List(String)) {
137
+
// Build clauses with tracked parameter index
138
+
let #(clauses, params, next_index) =
139
+
list.index_fold(sort_fields, #([], [], start_index), fn(acc, field, i) {
140
+
let #(acc_clauses, acc_params, param_index) = acc
141
+
142
+
// Build equality parts for prior fields
143
+
let #(equality_parts, equality_params, idx_after_eq) = case i {
144
+
0 -> #([], [], param_index)
145
+
_ -> {
146
+
list.index_fold(
147
+
list.take(sort_fields, i),
148
+
#([], [], param_index),
149
+
fn(eq_acc, prior_field, j) {
150
+
let #(eq_parts, eq_params, eq_idx) = eq_acc
151
+
let value = list_at(field_values, j) |> result.unwrap("")
152
+
let field_ref = build_cursor_field_reference(exec, prior_field.0)
153
+
let placeholder = executor.placeholder(exec, eq_idx)
154
+
let new_part = field_ref <> " = " <> placeholder
155
+
#(
156
+
list.append(eq_parts, [new_part]),
157
+
list.append(eq_params, [value]),
158
+
eq_idx + 1,
159
+
)
160
+
},
161
+
)
162
+
}
163
+
}
164
+
165
+
let value = list_at(field_values, i) |> result.unwrap("")
166
+
let comparison_op = get_comparison_operator(field.1, is_before)
167
+
let field_ref = build_cursor_field_reference(exec, field.0)
168
+
let placeholder = executor.placeholder(exec, idx_after_eq)
169
+
170
+
let comparison_part = field_ref <> " " <> comparison_op <> " " <> placeholder
171
+
let all_parts = list.append(equality_parts, [comparison_part])
172
+
let all_params = list.append(equality_params, [value])
173
+
174
+
let clause = "(" <> string.join(all_parts, " AND ") <> ")"
175
+
176
+
#(
177
+
list.append(acc_clauses, [clause]),
178
+
list.append(acc_params, all_params),
179
+
idx_after_eq + 1,
180
+
)
181
+
})
182
+
183
+
// Build final clause with all fields equal and CID comparison
184
+
let #(final_equality_parts, final_equality_params, idx_after_final_eq) =
185
+
list.index_fold(sort_fields, #([], [], next_index), fn(acc, field, j) {
186
+
let #(parts, params, idx) = acc
187
+
let value = list_at(field_values, j) |> result.unwrap("")
188
+
let field_ref = build_cursor_field_reference(exec, field.0)
189
+
let placeholder = executor.placeholder(exec, idx)
190
+
#(
191
+
list.append(parts, [field_ref <> " = " <> placeholder]),
192
+
list.append(params, [value]),
193
+
idx + 1,
194
+
)
195
+
})
196
+
197
+
let last_field = list.last(sort_fields) |> result.unwrap(#("", "desc"))
198
+
let cid_comparison_op = get_comparison_operator(last_field.1, is_before)
199
+
let cid_placeholder = executor.placeholder(exec, idx_after_final_eq)
200
+
201
+
let final_parts =
202
+
list.append(final_equality_parts, ["cid " <> cid_comparison_op <> " " <> cid_placeholder])
203
+
let final_params = list.append(final_equality_params, [cid])
204
+
205
+
let final_clause = "(" <> string.join(final_parts, " AND ") <> ")"
206
+
let all_clauses = list.append(clauses, [final_clause])
207
+
let all_params = list.append(params, final_params)
208
+
209
+
#(all_clauses, all_params)
210
+
}
211
+
```
212
+
213
+
**Step 3: Run build to verify syntax**
214
+
215
+
Run: `cd ~/code/quickslice/server && gleam build`
216
+
Expected: Compilation errors about callers (we'll fix in Task 3)
217
+
218
+
---
219
+
220
+
### Task 3: Update All Callers in records.gleam
221
+
222
+
**Files:**
223
+
- Modify: `server/src/database/repositories/records.gleam`
224
+
225
+
There are 5 places that call `build_cursor_where_clause`. Each needs to pass the current parameter count + 1 as the start_index.
226
+
227
+
**Step 1: Update get_by_collection_paginated (line ~548)**
228
+
229
+
Find lines 548-555 and change from:
230
+
231
+
```gleam
232
+
let #(cursor_where, cursor_params) =
233
+
pagination.build_cursor_where_clause(
234
+
exec,
235
+
decoded_cursor,
236
+
sort_by,
237
+
!is_forward,
238
+
)
239
+
```
240
+
241
+
To:
242
+
243
+
```gleam
244
+
let #(cursor_where, cursor_params) =
245
+
pagination.build_cursor_where_clause(
246
+
exec,
247
+
decoded_cursor,
248
+
sort_by,
249
+
!is_forward,
250
+
list.length(bind_values) + 1,
251
+
)
252
+
```
253
+
254
+
**Step 2: Update get_by_collection_paginated_with_where (line ~701)**
255
+
256
+
Find lines 701-708 and change from:
257
+
258
+
```gleam
259
+
let #(cursor_where, cursor_params) =
260
+
pagination.build_cursor_where_clause(
261
+
exec,
262
+
decoded_cursor,
263
+
sort_by,
264
+
!is_forward,
265
+
)
266
+
```
267
+
268
+
To:
269
+
270
+
```gleam
271
+
let #(cursor_where, cursor_params) =
272
+
pagination.build_cursor_where_clause(
273
+
exec,
274
+
decoded_cursor,
275
+
sort_by,
276
+
!is_forward,
277
+
list.length(bind_values) + 1,
278
+
)
279
+
```
280
+
281
+
**Step 3: Update get_by_reference_field_paginated (line ~941)**
282
+
283
+
Find lines 941-948 and change from:
284
+
285
+
```gleam
286
+
let #(cursor_where, cursor_params) =
287
+
pagination.build_cursor_where_clause(
288
+
exec,
289
+
decoded_cursor,
290
+
sort_by,
291
+
!is_forward,
292
+
)
293
+
```
294
+
295
+
To:
296
+
297
+
```gleam
298
+
let #(cursor_where, cursor_params) =
299
+
pagination.build_cursor_where_clause(
300
+
exec,
301
+
decoded_cursor,
302
+
sort_by,
303
+
!is_forward,
304
+
list.length(with_where_values) + 1,
305
+
)
306
+
```
307
+
308
+
**Step 4: Update get_by_dids_and_collection_paginated (line ~1297)**
309
+
310
+
Find lines 1297-1304 and change from:
311
+
312
+
```gleam
313
+
let #(cursor_where, cursor_params) =
314
+
pagination.build_cursor_where_clause(
315
+
exec,
316
+
decoded_cursor,
317
+
sort_by,
318
+
!is_forward,
319
+
)
320
+
```
321
+
322
+
To:
323
+
324
+
```gleam
325
+
let #(cursor_where, cursor_params) =
326
+
pagination.build_cursor_where_clause(
327
+
exec,
328
+
decoded_cursor,
329
+
sort_by,
330
+
!is_forward,
331
+
list.length(with_where_values) + 1,
332
+
)
333
+
```
334
+
335
+
**Step 5: Build to verify all callers are updated**
336
+
337
+
Run: `cd ~/code/quickslice/server && gleam build`
338
+
Expected: BUILD SUCCESS
339
+
340
+
**Step 6: Commit the fix**
341
+
342
+
```bash
343
+
cd ~/code/quickslice/server
344
+
git add src/database/queries/pagination.gleam src/database/repositories/records.gleam
345
+
git commit -m "fix: use numbered placeholders in cursor WHERE clause for PostgreSQL
346
+
347
+
The build_cursor_where_clause function was using literal '?' placeholders,
348
+
which works for SQLite but fails on PostgreSQL (which needs \$1, \$2, etc.).
349
+
350
+
Now accepts a start_index parameter and uses executor.placeholder() to
351
+
generate the correct format for each database dialect.
352
+
353
+
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>"
354
+
```
355
+
356
+
---
357
+
358
+
### Task 4: Update Unit Tests
359
+
360
+
**Files:**
361
+
- Modify: `server/test/pagination_test.gleam`
362
+
363
+
The existing tests check for `?` placeholders. They pass because tests use SQLite. We need to update tests to pass the new start_index parameter.
364
+
365
+
**Step 1: Update build_where_single_field_desc_test**
366
+
367
+
Find the test around line 272 and change:
368
+
369
+
```gleam
370
+
let #(sql, params) =
371
+
pagination.build_cursor_where_clause(exec, decoded, sort_by, False)
372
+
```
373
+
374
+
To:
375
+
376
+
```gleam
377
+
let #(sql, params) =
378
+
pagination.build_cursor_where_clause(exec, decoded, sort_by, False, 1)
379
+
```
380
+
381
+
**Step 2: Update build_where_single_field_asc_test**
382
+
383
+
Find the test around line 298 and change:
384
+
385
+
```gleam
386
+
let #(sql, params) =
387
+
pagination.build_cursor_where_clause(exec, decoded, sort_by, False)
388
+
```
389
+
390
+
To:
391
+
392
+
```gleam
393
+
let #(sql, params) =
394
+
pagination.build_cursor_where_clause(exec, decoded, sort_by, False, 1)
395
+
```
396
+
397
+
**Step 3: Update build_where_json_field_test**
398
+
399
+
Find the test around line 324 and change:
400
+
401
+
```gleam
402
+
let #(sql, params) =
403
+
pagination.build_cursor_where_clause(exec, decoded, sort_by, False)
404
+
```
405
+
406
+
To:
407
+
408
+
```gleam
409
+
let #(sql, params) =
410
+
pagination.build_cursor_where_clause(exec, decoded, sort_by, False, 1)
411
+
```
412
+
413
+
**Step 4: Update build_where_nested_json_field_test**
414
+
415
+
Find the test around line 345 and change:
416
+
417
+
```gleam
418
+
let #(sql, params) =
419
+
pagination.build_cursor_where_clause(exec, decoded, sort_by, False)
420
+
```
421
+
422
+
To:
423
+
424
+
```gleam
425
+
let #(sql, params) =
426
+
pagination.build_cursor_where_clause(exec, decoded, sort_by, False, 1)
427
+
```
428
+
429
+
**Step 5: Update build_where_multi_field_test**
430
+
431
+
Find the test around line 366 and change:
432
+
433
+
```gleam
434
+
let #(sql, params) =
435
+
pagination.build_cursor_where_clause(exec, decoded, sort_by, False)
436
+
```
437
+
438
+
To:
439
+
440
+
```gleam
441
+
let #(sql, params) =
442
+
pagination.build_cursor_where_clause(exec, decoded, sort_by, False, 1)
443
+
```
444
+
445
+
**Step 6: Update build_where_backward_test**
446
+
447
+
Find the test around line 398 and change:
448
+
449
+
```gleam
450
+
let #(sql, params) =
451
+
pagination.build_cursor_where_clause(exec, decoded, sort_by, True)
452
+
```
453
+
454
+
To:
455
+
456
+
```gleam
457
+
let #(sql, params) =
458
+
pagination.build_cursor_where_clause(exec, decoded, sort_by, True, 1)
459
+
```
460
+
461
+
**Step 7: Run tests**
462
+
463
+
Run: `cd ~/code/quickslice/server && gleam test`
464
+
Expected: All tests pass (SQLite uses `?` regardless of index, so assertions still work)
465
+
466
+
**Step 8: Commit test updates**
467
+
468
+
```bash
469
+
cd ~/code/quickslice/server
470
+
git add test/pagination_test.gleam
471
+
git commit -m "test: update pagination tests with start_index parameter
472
+
473
+
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>"
474
+
```
475
+
476
+
---
477
+
478
+
### Task 5: Manual Verification with MCP
479
+
480
+
**Step 1: Test pagination via quickslice MCP**
481
+
482
+
Run this GraphQL query:
483
+
484
+
```graphql
485
+
query {
486
+
gamesGamesgamesgamesgamesGame(first: 2) {
487
+
pageInfo {
488
+
hasNextPage
489
+
endCursor
490
+
}
491
+
edges {
492
+
node { name }
493
+
}
494
+
}
495
+
}
496
+
```
497
+
498
+
**Step 2: Test pagination with cursor**
499
+
500
+
Use the `endCursor` from step 1:
501
+
502
+
```graphql
503
+
query {
504
+
gamesGamesgamesgamesgamesGame(first: 2, after: "<endCursor>") {
505
+
pageInfo {
506
+
hasNextPage
507
+
endCursor
508
+
}
509
+
edges {
510
+
node { name }
511
+
}
512
+
}
513
+
}
514
+
```
515
+
516
+
Expected: Returns the NEXT 2 records (not empty, not the same as page 1)
517
+
518
+
**Step 3: Commit verification note (optional)**
519
+
520
+
If all works, the fix is complete.