Preserve code-only driver settings on DbConnection/DbDataSource paths

[alex-clickhouse]

Summary

Fixes #50. When a user configures the provider via UseClickHouse(DbConnection) or UseClickHouse(DbDataSource) using a ClickHouseClientSettings built in code, settings that have no connection-string representation were silently dropped — most visibly SkipServerCertificateValidation, which is why connecting to a server with a self-signed certificate failed under EF Core even though the same settings work with a bare ClickHouseClient.

Root cause

The driver's ClickHouseConnection.ConnectionString setter does Settings = new ClickHouseClientSettings(value) — it rebuilds settings purely from the connection string. Anything not representable as a connection-string key is lost on a round-trip: SkipServerCertificateValidation, BearerToken, HttpClient, HttpClientFactory, HttpClientName, LoggerFactory, EnableDebugMode, CustomHeaders, ApplicationInfo, and the parameter/read converters.

Two sites in ClickHouseRelationalConnection round-tripped through the string:

1. EnsureJoinUseNulls (called from Open/OpenAsync) — rewrote ConnectionString to inject join_use_nulls=1. This hit both the DbConnection and DbDataSource paths.
2. CreateMasterConnection (used by ClickHouseDatabaseCreator for CREATE/DROP DATABASE, i.e. EnsureCreated/EnsureDeleted/migrations) — rebuilt the master connection from the connection string. The same self-signed-cert user would still fail on database create/drop even with add aggregate method translator #1 fixed.

Fix

• EnsureJoinUseNulls now injects join_use_nulls by cloning Settings and setting CustomSettings["join_use_nulls"] = "1" for a ClickHouseConnection, rather than rewriting ConnectionString. The string rewrite remains only as a fallback for a non-ClickHouse DbConnection. The user opt-out (set_join_use_nulls=0) is still honored.
• CreateMasterConnection now clones the driver settings and only swaps Database = "default", handing back a context-owned ClickHouseConnection, instead of reconstructing from the connection string. ApplicationInfo (the lib User-Agent tag added on main) is preserved via the copy constructor.

Testing

• Added regression tests in ConnectionSettingsTests covering both fixed sites and both input paths, asserting SkipServerCertificateValidation, BearerToken, and CustomHeaders survive, plus that the join_use_nulls opt-out is preserved on the master path. These fail against pre-fix code.
• All 11 ConnectionSettingsTests pass against a real ClickHouse container.

Notes

The durable guard against reintroducing this class of bug is the TryGetClickHouseClientSettings helper (clone-the-settings-object pattern). Any future code that reconstructs a connection from .ConnectionString would reintroduce the defect; a full-codebase review found no other current instances.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[Copilot]

Pull request overview

This PR fixes a provider bug where configuring ClickHouse via UseClickHouse(DbConnection) or UseClickHouse(DbDataSource) could silently drop driver settings that have no connection-string representation (e.g., SkipServerCertificateValidation), by avoiding round-trips through DbConnection.ConnectionString and instead cloning/preserving ClickHouseClientSettings.

Changes:

• Update ClickHouseRelationalConnection.Open/OpenAsync to inject join_use_nulls via ClickHouseConnection.Settings.CustomSettings (with a connection-string fallback for non-ClickHouse connections).
• Update CreateMasterConnection() to clone driver settings and only switch Database = "default" instead of rebuilding settings from a connection string.
• Add regression tests ensuring code-only settings and join_use_nulls opt-out behavior are preserved across both DbConnection and DbDataSource configuration paths.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/EFCore.ClickHouse/Storage/Internal/ClickHouseRelationalConnection.cs	Preserves code-only driver settings by cloning settings for join_use_nulls injection and master connections.
test/EFCore.ClickHouse.Tests/ConnectionSettingsTests.cs	Adds regression coverage for preserving code-only settings and join_use_nulls opt-out across configuration paths.

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[alex-clickhouse]

Good catch — fixed in 45edc2d. The fallback now uses _dataSource?.ConnectionString ?? ConnectionString, so a non-ClickHouse DbDataSource (which sets no connection string on the EF options) builds a valid master connection string. Added CreateMasterConnection_NonClickHouseDataSource_UsesDataSourceConnectionString to cover it.

[alex-clickhouse]

Fixed in 45edc2d — reworded the summary to state that the setting is recorded on ClickHouseConnection.Settings, with the connection-string path used only as a fallback for a non-ClickHouse DbConnection.