BE-416: Add Constant::JsonNull, remove Constant::String, add From impls

[TimDiekmann]

🌟 What is the purpose of this PR?

Cleans up the Constant enum in the PostgreSQL query expression system by removing the String variant (string literals should go through Parameter to avoid embedding literals in SQL) and adding ergonomic From trait impls for the remaining variants.

🔗 Related links

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🚫 Blocked by

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🔍 What does this change?

• Removes Constant::String — string values must go through Parameter
• Implements From<bool> and From<u32> for ergonomic constant creation
• Improves UnsignedInteger transpilation to use fmt::Display
• Updates tests to use the new From impls

Pre-Merge Checklist 🚀

🚢 Has this modified a publishable library?

This PR:

• does not modify any publishable blocks or libraries, or modifications do not need publishing

📜 Does this require a change to the docs?

The changes in this PR:

• are internal and do not require a docs change

🕸️ Does this require a change to the Turbo Graph?

The changes in this PR:

• do not affect the execution graph

⚠️ Known issues

🐾 Next steps

🛡 What tests cover this?

• Existing unit tests for case expressions, array operations, and transpilation functionality

❓ How to test this?

1. Checkout the branch
2. Run cargo nextest run --package hash-graph-postgres-store -E 'test(expression)'

📹 Demo

[cursor]

PR Summary

Medium Risk
Touches SQL generation semantics and removes a public enum variant, so downstream code may break at compile time and query output can change if callers previously relied on inlined string literals.

Overview
Refactors constant handling in the Postgres query expression layer. Constant::String is removed so string literals are no longer directly embedded into generated SQL, pushing callers toward Expression::Parameter for text values.

Adds Constant::JsonNull (transpiles to 'null'::jsonb) plus From<bool>/From<u32> impls to simplify constant construction, and adjusts transpilation/tests accordingly (including switching array-literal test cases from string constants to parameters).

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[TimDiekmann]

• BE-418: Add ROW constructor expression to PostgreSQL query builder #8470
• BE-417: Refactor PostgreSQL query expressions to use binary/variadic operators instead of functions #8469
• BE-416: Add Constant::JsonNull, remove Constant::String, add From impls #8468 👈 (View in Graphite)
• BE-415: Unify Condition and Expression types in PostgreSQL query builder #8467
• main

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[augmentcode]

🤖 Augment PR Summary

Summary: Refactors the Postgres expression "constant" representation to better model SQL literals.

Changes:

• Renamed Constant::String to Constant::Text for clearer semantics
• Added a Constant::Null variant and transpilation to the SQL NULL literal
• Removed Hash derivation from Constant
• Implemented From conversions (bool, &'static str, u32) for more ergonomic construction
• Updated transpilation formatting for unsigned integers and refactored affected tests to use the new conversions

Technical Notes: Constants are still directly inlined into SQL during transpilation (vs parameters), so correctness/safety of literal formatting remains important.

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[augmentcode]

Review completed. 2 suggestions posted.

Comment augment review to trigger a new review at any time.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.59%. Comparing base (bc6e591) to head (358f119).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8468   +/-   ##
=======================================
  Coverage   62.59%   62.59%           
=======================================
  Files        1296     1296           
  Lines      131048   131054    +6     
  Branches     5488     5488           
=======================================
+ Hits        82032    82038    +6     
  Misses      48106    48106           
  Partials      910      910           

Flag	Coverage Δ
apps.hash-ai-worker-ts	1.40% <ø> (ø)
apps.hash-api	0.00% <ø> (ø)
local.hash-graph-sdk	7.78% <ø> (ø)
local.hash-isomorphic-utils	0.00% <ø> (ø)
rust.hash-graph-api	2.86% <ø> (ø)
rust.hash-graph-postgres-store	27.47% <100.00%> (+0.02%)	⬆️

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Your organization requires reapproval when changes are made, so Graphite has dismissed approvals. See the output of git range-diff at https://github.com/hashintel/hash/actions/runs/22310452345

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[github-actions]

Benchmark results

@rust/hash-graph-benches – Integrations

policy_resolution_large

Function	Value	Mean	Flame graphs
resolve_policies_for_actor	user: empty, selectivity: high, policies: 2002	$$26.7 \mathrm{ms} \pm 186 \mathrm{μs}\left({\color{gray}1.46 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: empty, selectivity: low, policies: 1	$$2.79 \mathrm{ms} \pm 16.9 \mathrm{μs}\left({\color{gray}1.08 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: empty, selectivity: medium, policies: 1001	$$12.2 \mathrm{ms} \pm 67.5 \mathrm{μs}\left({\color{gray}2.93 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: seeded, selectivity: high, policies: 3314	$$39.2 \mathrm{ms} \pm 305 \mathrm{μs}\left({\color{gray}1.49 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: seeded, selectivity: low, policies: 1	$$12.3 \mathrm{ms} \pm 66.6 \mathrm{μs}\left({\color{gray}2.83 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: seeded, selectivity: medium, policies: 1526	$$21.6 \mathrm{ms} \pm 123 \mathrm{μs}\left({\color{gray}2.74 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: system, selectivity: high, policies: 2078	$$27.4 \mathrm{ms} \pm 151 \mathrm{μs}\left({\color{gray}1.19 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: system, selectivity: low, policies: 1	$$3.14 \mathrm{ms} \pm 23.3 \mathrm{μs}\left({\color{gray}3.13 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: system, selectivity: medium, policies: 1033	$$13.0 \mathrm{ms} \pm 81.5 \mathrm{μs}\left({\color{gray}3.91 \mathrm{\%}}\right) $$	Flame Graph

policy_resolution_medium

Function	Value	Mean	Flame graphs
resolve_policies_for_actor	user: empty, selectivity: high, policies: 102	$$3.12 \mathrm{ms} \pm 21.4 \mathrm{μs}\left({\color{gray}0.505 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: empty, selectivity: low, policies: 1	$$2.39 \mathrm{ms} \pm 13.8 \mathrm{μs}\left({\color{gray}0.088 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: empty, selectivity: medium, policies: 51	$$2.71 \mathrm{ms} \pm 18.1 \mathrm{μs}\left({\color{gray}-0.724 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: seeded, selectivity: high, policies: 269	$$4.43 \mathrm{ms} \pm 23.3 \mathrm{μs}\left({\color{gray}-0.473 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: seeded, selectivity: low, policies: 1	$$2.95 \mathrm{ms} \pm 21.0 \mathrm{μs}\left({\color{gray}1.46 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: seeded, selectivity: medium, policies: 107	$$3.39 \mathrm{ms} \pm 20.6 \mathrm{μs}\left({\color{gray}-0.075 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: system, selectivity: high, policies: 133	$$3.79 \mathrm{ms} \pm 32.6 \mathrm{μs}\left({\color{gray}1.24 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: system, selectivity: low, policies: 1	$$2.84 \mathrm{ms} \pm 29.5 \mathrm{μs}\left({\color{gray}1.65 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: system, selectivity: medium, policies: 63	$$3.33 \mathrm{ms} \pm 20.7 \mathrm{μs}\left({\color{gray}0.146 \mathrm{\%}}\right) $$	Flame Graph

policy_resolution_none

Function	Value	Mean	Flame graphs
resolve_policies_for_actor	user: empty, selectivity: high, policies: 2	$$2.17 \mathrm{ms} \pm 11.9 \mathrm{μs}\left({\color{gray}1.30 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: empty, selectivity: low, policies: 1	$$2.13 \mathrm{ms} \pm 10.5 \mathrm{μs}\left({\color{gray}0.337 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: empty, selectivity: medium, policies: 1	$$2.24 \mathrm{ms} \pm 16.1 \mathrm{μs}\left({\color{gray}1.62 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: system, selectivity: high, policies: 8	$$2.51 \mathrm{ms} \pm 18.8 \mathrm{μs}\left({\color{red}6.25 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: system, selectivity: low, policies: 1	$$2.31 \mathrm{ms} \pm 17.5 \mathrm{μs}\left({\color{gray}3.80 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: system, selectivity: medium, policies: 3	$$2.56 \mathrm{ms} \pm 19.8 \mathrm{μs}\left({\color{gray}3.16 \mathrm{\%}}\right) $$	Flame Graph

policy_resolution_small

Function	Value	Mean	Flame graphs
resolve_policies_for_actor	user: empty, selectivity: high, policies: 52	$$2.48 \mathrm{ms} \pm 12.5 \mathrm{μs}\left({\color{gray}-0.217 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: empty, selectivity: low, policies: 1	$$2.24 \mathrm{ms} \pm 14.2 \mathrm{μs}\left({\color{gray}2.66 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: empty, selectivity: medium, policies: 25	$$2.36 \mathrm{ms} \pm 15.8 \mathrm{μs}\left({\color{gray}2.49 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: seeded, selectivity: high, policies: 94	$$2.82 \mathrm{ms} \pm 24.8 \mathrm{μs}\left({\color{gray}0.244 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: seeded, selectivity: low, policies: 1	$$2.45 \mathrm{ms} \pm 15.3 \mathrm{μs}\left({\color{gray}-0.233 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: seeded, selectivity: medium, policies: 26	$$2.58 \mathrm{ms} \pm 11.8 \mathrm{μs}\left({\color{gray}-0.969 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: system, selectivity: high, policies: 66	$$2.72 \mathrm{ms} \pm 14.6 \mathrm{μs}\left({\color{gray}1.07 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: system, selectivity: low, policies: 1	$$2.39 \mathrm{ms} \pm 12.8 \mathrm{μs}\left({\color{gray}-1.531 \mathrm{\%}}\right) $$	Flame Graph
resolve_policies_for_actor	user: system, selectivity: medium, policies: 29	$$2.58 \mathrm{ms} \pm 14.1 \mathrm{μs}\left({\color{gray}-1.610 \mathrm{\%}}\right) $$	Flame Graph

read_scaling_complete

Function	Value	Mean	Flame graphs
entity_by_id;one_depth	1 entities	$$36.0 \mathrm{ms} \pm 288 \mathrm{μs}\left({\color{gray}4.57 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;one_depth	10 entities	$$72.9 \mathrm{ms} \pm 330 \mathrm{μs}\left({\color{gray}-1.111 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;one_depth	25 entities	$$38.7 \mathrm{ms} \pm 195 \mathrm{μs}\left({\color{gray}1.44 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;one_depth	5 entities	$$43.1 \mathrm{ms} \pm 230 \mathrm{μs}\left({\color{gray}0.711 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;one_depth	50 entities	$$48.5 \mathrm{ms} \pm 208 \mathrm{μs}\left({\color{gray}-0.745 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;two_depth	1 entities	$$37.8 \mathrm{ms} \pm 292 \mathrm{μs}\left({\color{gray}4.26 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;two_depth	10 entities	$$416 \mathrm{ms} \pm 1.01 \mathrm{ms}\left({\color{gray}-0.021 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;two_depth	25 entities	$$87.7 \mathrm{ms} \pm 415 \mathrm{μs}\left({\color{gray}-1.219 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;two_depth	5 entities	$$87.4 \mathrm{ms} \pm 469 \mathrm{μs}\left({\color{gray}-2.898 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;two_depth	50 entities	$$279 \mathrm{ms} \pm 1.15 \mathrm{ms}\left({\color{red}7.31 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;zero_depth	1 entities	$$13.5 \mathrm{ms} \pm 120 \mathrm{μs}\left({\color{gray}-4.208 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;zero_depth	10 entities	$$13.0 \mathrm{ms} \pm 67.7 \mathrm{μs}\left({\color{lightgreen}-7.401 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;zero_depth	25 entities	$$13.4 \mathrm{ms} \pm 71.3 \mathrm{μs}\left({\color{gray}-2.172 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;zero_depth	5 entities	$$13.0 \mathrm{ms} \pm 73.6 \mathrm{μs}\left({\color{gray}-4.545 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id;zero_depth	50 entities	$$15.8 \mathrm{ms} \pm 85.5 \mathrm{μs}\left({\color{lightgreen}-5.002 \mathrm{\%}}\right) $$	Flame Graph

read_scaling_linkless

Function	Value	Mean	Flame graphs
entity_by_id	1 entities	$$12.8 \mathrm{ms} \pm 66.0 \mathrm{μs}\left({\color{lightgreen}-6.737 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id	10 entities	$$12.9 \mathrm{ms} \pm 51.4 \mathrm{μs}\left({\color{gray}-3.365 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id	100 entities	$$12.9 \mathrm{ms} \pm 57.4 \mathrm{μs}\left({\color{gray}-3.307 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id	1000 entities	$$13.8 \mathrm{ms} \pm 77.4 \mathrm{μs}\left({\color{lightgreen}-5.057 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id	10000 entities	$$20.9 \mathrm{ms} \pm 126 \mathrm{μs}\left({\color{lightgreen}-5.333 \mathrm{\%}}\right) $$	Flame Graph

representative_read_entity

Function	Value	Mean	Flame graphs
entity_by_id	entity type ID: https://blockprotocol.org/@alice/types/entity-type/block/v/1	$$28.2 \mathrm{ms} \pm 272 \mathrm{μs}\left({\color{lightgreen}-6.147 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id	entity type ID: https://blockprotocol.org/@alice/types/entity-type/book/v/1	$$27.4 \mathrm{ms} \pm 304 \mathrm{μs}\left({\color{lightgreen}-9.762 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id	entity type ID: https://blockprotocol.org/@alice/types/entity-type/building/v/1	$$27.4 \mathrm{ms} \pm 262 \mathrm{μs}\left({\color{lightgreen}-9.147 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id	entity type ID: https://blockprotocol.org/@alice/types/entity-type/organization/v/1	$$27.5 \mathrm{ms} \pm 285 \mathrm{μs}\left({\color{lightgreen}-8.754 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id	entity type ID: https://blockprotocol.org/@alice/types/entity-type/page/v/2	$$28.2 \mathrm{ms} \pm 313 \mathrm{μs}\left({\color{gray}-3.477 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id	entity type ID: https://blockprotocol.org/@alice/types/entity-type/person/v/1	$$28.8 \mathrm{ms} \pm 373 \mathrm{μs}\left({\color{gray}-1.337 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id	entity type ID: https://blockprotocol.org/@alice/types/entity-type/playlist/v/1	$$28.2 \mathrm{ms} \pm 263 \mathrm{μs}\left({\color{lightgreen}-5.163 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id	entity type ID: https://blockprotocol.org/@alice/types/entity-type/song/v/1	$$27.3 \mathrm{ms} \pm 274 \mathrm{μs}\left({\color{lightgreen}-8.165 \mathrm{\%}}\right) $$	Flame Graph
entity_by_id	entity type ID: https://blockprotocol.org/@alice/types/entity-type/uk-address/v/1	$$28.7 \mathrm{ms} \pm 300 \mathrm{μs}\left({\color{gray}-0.485 \mathrm{\%}}\right) $$	Flame Graph

representative_read_entity_type

Function	Value	Mean	Flame graphs
get_entity_type_by_id	Account ID: bf5a9ef5-dc3b-43cf-a291-6210c0321eba	$$6.88 \mathrm{ms} \pm 54.7 \mathrm{μs}\left({\color{gray}-0.812 \mathrm{\%}}\right) $$	Flame Graph

representative_read_multiple_entities

Function	Value	Mean	Flame graphs
entity_by_property	traversal_paths=0	0	$$92.4 \mathrm{ms} \pm 547 \mathrm{μs}\left({\color{gray}-1.137 \mathrm{\%}}\right) $$
entity_by_property	traversal_paths=255	1,resolve_depths=inherit:1;values:255;properties:255;links:127;link_dests:126;type:true	$$137 \mathrm{ms} \pm 681 \mathrm{μs}\left({\color{gray}1.90 \mathrm{\%}}\right) $$
entity_by_property	traversal_paths=2	1,resolve_depths=inherit:0;values:0;properties:0;links:0;link_dests:0;type:false	$$99.4 \mathrm{ms} \pm 494 \mathrm{μs}\left({\color{gray}0.614 \mathrm{\%}}\right) $$
entity_by_property	traversal_paths=2	1,resolve_depths=inherit:0;values:0;properties:0;links:1;link_dests:0;type:true	$$105 \mathrm{ms} \pm 491 \mathrm{μs}\left({\color{gray}-0.160 \mathrm{\%}}\right) $$
entity_by_property	traversal_paths=2	1,resolve_depths=inherit:0;values:0;properties:2;links:1;link_dests:0;type:true	$$114 \mathrm{ms} \pm 565 \mathrm{μs}\left({\color{gray}0.433 \mathrm{\%}}\right) $$
entity_by_property	traversal_paths=2	1,resolve_depths=inherit:0;values:2;properties:2;links:1;link_dests:0;type:true	$$119 \mathrm{ms} \pm 582 \mathrm{μs}\left({\color{gray}-0.309 \mathrm{\%}}\right) $$
link_by_source_by_property	traversal_paths=0	0	$$86.5 \mathrm{ms} \pm 482 \mathrm{μs}\left({\color{gray}-1.645 \mathrm{\%}}\right) $$
link_by_source_by_property	traversal_paths=255	1,resolve_depths=inherit:1;values:255;properties:255;links:127;link_dests:126;type:true	$$111 \mathrm{ms} \pm 526 \mathrm{μs}\left({\color{gray}0.007 \mathrm{\%}}\right) $$
link_by_source_by_property	traversal_paths=2	1,resolve_depths=inherit:0;values:0;properties:0;links:0;link_dests:0;type:false	$$92.2 \mathrm{ms} \pm 464 \mathrm{μs}\left({\color{gray}-2.039 \mathrm{\%}}\right) $$
link_by_source_by_property	traversal_paths=2	1,resolve_depths=inherit:0;values:0;properties:0;links:1;link_dests:0;type:true	$$99.9 \mathrm{ms} \pm 460 \mathrm{μs}\left({\color{gray}-0.143 \mathrm{\%}}\right) $$
link_by_source_by_property	traversal_paths=2	1,resolve_depths=inherit:0;values:0;properties:2;links:1;link_dests:0;type:true	$$103 \mathrm{ms} \pm 522 \mathrm{μs}\left({\color{gray}0.574 \mathrm{\%}}\right) $$
link_by_source_by_property	traversal_paths=2	1,resolve_depths=inherit:0;values:2;properties:2;links:1;link_dests:0;type:true	$$103 \mathrm{ms} \pm 523 \mathrm{μs}\left({\color{gray}-0.174 \mathrm{\%}}\right) $$

scenarios

Function	Value	Mean	Flame graphs
full_test	query-limited	$$127 \mathrm{ms} \pm 611 \mathrm{μs}\left({\color{gray}4.29 \mathrm{\%}}\right) $$	Flame Graph
full_test	query-unlimited	$$125 \mathrm{ms} \pm 556 \mathrm{μs}\left({\color{red}6.25 \mathrm{\%}}\right) $$	Flame Graph
linked_queries	query-limited	$$90.7 \mathrm{ms} \pm 477 \mathrm{μs}\left({\color{gray}0.269 \mathrm{\%}}\right) $$	Flame Graph
linked_queries	query-unlimited	$$548 \mathrm{ms} \pm 3.03 \mathrm{ms}\left({\color{gray}-4.022 \mathrm{\%}}\right) $$	Flame Graph