Scan: ExpressionAttributeValues without an expression answers with a ": FilterExpression is null" suffix the service does not send

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@LeeroyHannigan 已经在做这个了。

开始于 2026年11月2日。

  • #765 来自 @LeeroyHannigan —— 未关闭

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技术栈
rust, sqlite
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database

调研方向

从 crates/core/src/expression/resolver.rs 中的 validate_expression_param_usage（约第 223 行）开始，它根据接收到的可携带值的参数列表构建后缀。然后查看 crates/engine/src/scan.rs 中的 handle_scan（第 109 到 115 行），它传入了 [ExpressionKind::Filter]。完成的标准是：带有 ExpressionAttributeValues 且没有 FilterExpression 的 Scan 返回的消息中不再包含 : FilterExpression is null 后缀，同时其他调用方的行为保持不变。请查看现有 Scan 验证测试中的预期文本。

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描述

A Scan that carries ExpressionAttributeValues and no FilterExpression answers ExpressionAttributeValues can only be specified when using expressions: FilterExpression is null. The service's message ends after expressions.

Measured against Amazon DynamoDB in us-east-1 on 31 October 2026, each request twice, both answers identical. Table pk S HASH, sk S RANGE with three items. Eight Scan requests, each with "ExpressionAttributeValues": {":d": v} and no FilterExpression:

v Other fields Service ExtendDB main f49c5f823 (SQLite, release build)
{"N": "1"} none ValidationException: ExpressionAttributeValues can only be specified when using expressions ValidationException: ExpressionAttributeValues can only be specified when using expressions: FilterExpression is null
{"N": "1"} inside 1, 2, 10, 30 and 31 nested L values (five requests) none the same the same
{"M": {"k": {"N": "1"}}} none the same the same
{"N": "1"} "ProjectionExpression": "a" the same the same

The service sends no suffix in any of the eight. A ninth request with 32 nested L values answers the nesting text on the service (#564), so the service checks nesting before it checks for values without an expression.

Where the suffix comes from

validate_expression_param_usage in crates/core/src/expression/resolver.rs (line 223) builds the message from the value_expr_params list its caller passes: no suffix for an empty list, : <param> is null for one entry, : <a> and <b> are null for more. Its doc comment states that the service lists the value-capable expression parameters of the API and that the empty list matches Query. handle_scan passes &[ExpressionKind::Filter] (crates/engine/src/scan.rs, line 109 to 115), so Scan gets the FilterExpression is null suffix. The other callers:

Caller List passed Suffix produced
Scan (scan.rs 109) [Filter] : FilterExpression is null
Query (query.rs 222) [] none
PutItem (put_item.rs 112) [Condition] : ConditionExpression is null
DeleteItem (delete_item.rs 71) [Condition] : ConditionExpression is null
UpdateItem (update_item.rs 126) [Update, Condition] : UpdateExpression and ConditionExpression are null
GetItem (get_item.rs 45), BatchGetItem (batch_get_item.rs 73) [] (names only) none

The 31 October measurement covers Scan only. Query's no-suffix answer on main (ExpressionAttributeValues can only be specified when using expressions, sent with KeyConditions and no expression) was not measured on the service on that date; the doc comment states it matches the service. The PutItem, DeleteItem and UpdateItem suffixes were not measured on 31 October, so this issue makes no claim about them. The suffix text was added in d4b60e0be (3 June 2026) with the Scan caller in 006cc6e13.

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