[alaricd]

Summary

DbType.Decimal and DbType.DateTime2 have no entry in ClrToDuckDBConverter.ValueCreators. A parameter declared with either type falls through to NativeMethods.Value.DuckDBCreateVarchar(item.ToString()), so the value is sent as text in the current culture. Under fr-FR or de-DE, a declared decimal is sent as 1234,5:

Statement (DuckDB.NET 1.5.6.1, de-DE)	DbType.Decimal, Value = 1234.5m
INSERT into a VARCHAR column	stores 1234,5
INSERT into a DOUBLE column	Conversion Error: Could not convert string '1234,5' to DOUBLE
SELECT ?	returns the string 1234,5, not a decimal

A DECIMAL column is not affected, because the target type routes the value through (DuckDBType.Decimal, decimal value) first.

Today this mostly stays hidden because a decimal value infers DbType.Currency, which does have a converter. Once #369 lets an explicit DbType survive assigning Value, every caller that sets DbType.Decimal hits this path.

Changes

• DbType.Decimal gets a converter: a decimal is sent as a DECIMAL, exactly like DbType.Currency. Any other value keeps the previous fallback, so DbType.Decimal with an int still works.
• DbType.DateTime2 is sent like DbType.DateTime (a TIMESTAMP). Any other value keeps the previous fallback.
• A decimal value now infers DbType.Decimal instead of DbType.Currency. This matches the ADO.NET inference table and DuckDB.NET's own GetSchema("DataTypes") (Support ADO.NET schema data types and metadata probing #364), which maps DECIMAL to System.Decimal. Binding does not change: both types send the same DECIMAL value, and DbType.Currency keeps working when set explicitly.

Tests

• DecimalValueInfersDbTypeDecimal
• ExplicitDecimalDbTypeIsSentAsADecimalInAnyCulture (Decimal and Currency, under fr-FR: SELECT ?, a VARCHAR column and a DOUBLE column)
• ExplicitDecimalDbTypeWithAnIntegerValueIsStillSent
• ExplicitDateTime2DbTypeIsSentAsATimestampInAnyCulture (de-DE)
• ExplicitDateTime2DbTypeWithATextValueIsStillSent

Three tests failed before the change (the inference, the Decimal case and DateTime2); the Currency case and the two fallback guards passed before and after. The full DuckDB.NET.Test suite passes locally (net8.0), including the connection stress tests, because the change touches PreparedStatement/. The new tests passed 5 runs in a row.

Found by pengdows.AdoNetApiTest.conformance (Bind_works_with_values_of_their_own_DbType_in_any_culture, DbType_is_inferred_from_Value).

🤖 Generated with Claude Code

[coveralls]

Coverage Report for CI Build 39939109057

Coverage increased (+0.08%) to 92.874%

Details

• Coverage increased (+0.08%) from the base build.
• Patch coverage: 7 of 7 lines across 2 files are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	4276
Covered Lines:	4036
Line Coverage:	94.39%
Relevant Branches:	2572
Covered Branches:	2324
Branch Coverage:	90.36%
Branches in Coverage %:	Yes
Coverage Strength:	973373.88 hits per line

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💛 - Coveralls