(fix) Prevent better-auth from converting dates to ISO strings

[juliesaia]

This PR enables supportsDates in the adapter config.

With supportsDates: false, better-auth automatically converts dates to ISO strings (see @better-auth/core/src/db/adapter/factory.ts). This breaks all the logic in this package that relies on instanceof Date to convert them to timestamp numbers instead.

With supportsDates: true, the existing logic to convert to timestamps can run.

There's probably more bugs downstream of this, but the one I came across was the reset password flow not working. By default better-auth cleans all expired verification tokens when fetching a token. With the broken logic, it was trying to do lt: '2025-12-20... which was always true. So when the user tries to submit the token to reset their password, its already deleted...

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Walkthrough

The convex adapter configuration is updated to set supportsDates to true, enabling better-auth to apply custom date transforms that convert dates to numbers instead of ISO strings, while existing custom transform logic remains in place.

Changes

Cohort / File(s)	Summary
Convex adapter date support src/client/adapter.ts	Set supportsDates configuration to true to enable date-to-number transformations via better-auth's custom date handlers

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

🐰 A tiny flag flipped true with care,
Dates now dance through numeric air,
Numbers bloom where ISO strings once grew,
The rabbit hops—one change will do! ✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: enabling supportsDates to prevent better-auth from converting dates to ISO strings, which aligns with the core fix in the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

src/client/adapter.ts (1)

87-97: Date handling is consistent with custom transforms.

The parseWhere function correctly converts Date instances to timestamps using getTime(), which aligns with the custom transform behavior. This ensures consistent date handling throughout the adapter.

Optional: Consider adding validation for invalid dates in both parseWhere and the custom transforms, since new Date(invalidValue).getTime() returns NaN. However, this is a pre-existing consideration and can be addressed separately if needed.

📜 Review details

Configuration used: defaults

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 920ec5e and f833a0b.

📒 Files selected for processing (1)

• src/client/adapter.ts (1 hunks)

🧰 Additional context used

🧠 Learnings (7)

📚 Learning: 2025-12-20T00:20:00.408Z

Learnt from: CR
Repo: get-convex/better-auth PR: 0
File: examples/next/.cursor/rules/convex_rules.mdc:0-0
Timestamp: 2025-12-20T00:20:00.408Z
Learning: Applies to examples/next/convex/**/*.{ts,tsx} : Use `v.int64()` instead of the deprecated `v.bigint()` for representing signed 64-bit integers

Applied to files:

• src/client/adapter.ts

📚 Learning: 2025-12-20T00:20:00.408Z

Learnt from: CR
Repo: get-convex/better-auth PR: 0
File: examples/next/.cursor/rules/convex_rules.mdc:0-0
Timestamp: 2025-12-20T00:20:00.408Z
Learning: Applies to examples/next/convex/**/*.{ts,tsx} : ALWAYS use the new function syntax for Convex functions with `query`, `mutation`, or `action` decorators, including `args`, `returns`, and `handler` properties

Applied to files:

• src/client/adapter.ts

📚 Learning: 2025-12-20T00:20:00.408Z

Learnt from: CR
Repo: get-convex/better-auth PR: 0
File: examples/next/.cursor/rules/convex_rules.mdc:0-0
Timestamp: 2025-12-20T00:20:00.408Z
Learning: Applies to examples/next/convex/**/*.{ts,tsx} : Convex storage stores items as `Blob` objects. You must convert all items to/from a `Blob` when using Convex storage

Applied to files:

• src/client/adapter.ts

📚 Learning: 2025-12-20T00:20:00.408Z

Learnt from: CR
Repo: get-convex/better-auth PR: 0
File: examples/next/.cursor/rules/convex_rules.mdc:0-0
Timestamp: 2025-12-20T00:20:00.408Z
Learning: Applies to examples/next/convex/**/*.{ts,tsx} : Use `v.record()` for defining record types; `v.map()` and `v.set()` are not supported in Convex

Applied to files:

• src/client/adapter.ts

📚 Learning: 2025-12-16T22:34:45.580Z

Learnt from: CR
Repo: get-convex/better-auth PR: 0
File: .cursor/rules/convex_rules.mdc:0-0
Timestamp: 2025-12-16T22:34:45.580Z
Learning: Applies to convex/schema.ts : System fields `_creationTime` and `_id` are automatically added to all documents. Use validators `v.number()` for `_creationTime` and `v.id(tableName)` for `_id`

Applied to files:

• src/client/adapter.ts

📚 Learning: 2025-12-20T00:20:00.408Z

Learnt from: CR
Repo: get-convex/better-auth PR: 0
File: examples/next/.cursor/rules/convex_rules.mdc:0-0
Timestamp: 2025-12-20T00:20:00.408Z
Learning: Applies to examples/next/convex/**/*.{ts,tsx} : By default Convex always returns documents in ascending `_creationTime` order

Applied to files:

• src/client/adapter.ts

📚 Learning: 2025-12-16T22:34:45.581Z

Learnt from: CR
Repo: get-convex/better-auth PR: 0
File: .cursor/rules/convex_rules.mdc:0-0
Timestamp: 2025-12-16T22:34:45.581Z
Learning: Applies to convex/**/*.ts : By default Convex always returns documents in ascending `_creationTime` order. Use `.order('asc')` or `.order('desc')` to pick the order

Applied to files:

• src/client/adapter.ts

🔇 Additional comments (1)

src/client/adapter.ts (1)

132-149: Fix looks correct and addresses the root cause.

The change from supportsDates: false to supportsDates: true properly enables the custom date transformation logic. With this change:

• better-auth's date transformations are applied before customTransformInput, allowing the custom transforms to convert dates to numeric timestamps
• The parseWhere function (line 89) can successfully use instanceof Date checks
• Custom transforms convert dates to millisecond timestamps, which Convex supports natively
• Date comparisons work correctly as numeric operations instead of string comparisons

This fixes the reported reset password flow failure where ISO string comparisons like lt: '2025-12-20...' were incorrectly evaluating.

[l3dotdev]

Related #206

[erquhart]

Thanks for opening this @juliesaia! This was an upstream bug, fixed in better-auth 1.4.8, and we now test for proper date handling as well. We do want to keep supportsDates: false because Convex doesn't support actual JS dates, so it's better that they not be passed to the adapter in the first place.