Document ConfigureDbContext method and AddDbContext precedence changes in EF Core 8.0

[Copilot]

This PR documents the ConfigureDbContext method and clarifies the breaking change in EF Core 8.0 regarding multiple AddDbContext calls.

Overview

This PR addresses two related issues:

• Issue Document ConfigureDbContext  #4588: Document ConfigureDbContext method
• Issue Document DbContextOptions service registration breaking change #4923: Clarify breaking changes in EF Core 8.0 for multiple AddDbContext calls

Breaking Changes Documentation (EF Core 8.0)

Enhanced the breaking changes documentation for multiple AddDbContext calls with:

• Streamlined descriptions: Removed redundant code examples from "Old behavior" and "New behavior" sections for better readability
• Clear rationale: Updated "Why" section to explain that the change was made to be consistent with the new ConfigureDbContext method, with a link to detailed documentation
• Comprehensive mitigations: Added four different migration strategies:
  1. Reordering registrations to place desired configuration last
  2. Removing conflicting registrations when possible
  3. Using conditional registration checks
  4. Using the new ConfigureDbContext method (EF Core 9.0+)

ConfigureDbContext Documentation (EF Core 9.0)

Added comprehensive documentation for the ConfigureDbContext method introduced in EF Core 9.0:

Key Capabilities

• Configuration composition: Enables adding non-conflicting configuration
• Reusable components: Perfect for creating testing utilities or library configurations
• Provider-agnostic options: Add logging, interceptors, or other options without knowing the database provider
• Provider-specific configuration: Apply provider-specific options without connection strings using methods like ConfigureSqlEngine

Documentation Includes

• API reference link to ConfigureDbContext method
• Basic usage examples showing configuration composition
• Provider-specific configuration patterns without connection strings
• Configuration precedence behavior with multiple calls
• Note about provider replacement limitations

Sample Code

• Integrated ConfigureDbContext sample code into the main ConfiguringDbContext.csproj project
• Sample code is now in ConfigureDbContextSample.cs in the main samples directory
• All samples compile and run successfully with .NET 9.0 and EF Core 9.0
• Clean code structure with proper region boundaries excluding the service provider instantiation
• Fixed nullable annotation warnings and entry point conflicts
• All package references updated to version 9.0.0 for consistency
• Sample class properly named as ConfigureDbContextSample

Technical Clarifications

• ConfigureDbContext availability: Introduced in EF Core 9.0 (not 8.0)
• Breaking change: Multiple AddDbContext calls now use last-wins precedence (changed in EF Core 8.0)
• Configuration composition: Non-conflicting options (logging, interceptors) compose together; conflicting options (providers) use last-wins
• Design consistency: The EF Core 8.0 breaking change was made to be consistent with the future ConfigureDbContext method
• Provider replacement: Configuring a different provider doesn't remove previous provider configuration; a note is included

Fixes #4588
Fixes #4923

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Document ConfigureDbContext </issue_title>
<issue_description>Also document the minor breaking change when AddDbContext is called multiple times with different options, see dotnet/efcore#32518</issue_description>

<agent_instructions>Note that the breaking change is in 8.0</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes #4588

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[AndriySvyryd]

https://gh.io/copilot-coding-agent-docs Update progress by changing the PR description to a nicely formatted summary of the changes that includes fixing #4923

[Copilot]

https://gh.io/copilot-coding-agent-docs Update progress by changing the PR description to a nicely formatted summary of the changes that includes fixing https://github.com/dotnet/EntityFramework.Docs/...

Updated PR description with a nicely formatted summary that includes fixing both issues #4588 and #4923.

[roji]

This definitely doesn't seem like the first thing to document on this page, above "Basic DbContext initialization with 'new'". IIUC (and as documented), ConfigureDbContext is for reusable libraries/components (like Aspire), and so is not an end-user API. As such it maybe merits a short note at the very bottom, but nothing like this at the very top - this would confuse any beginner user coming here.

(FWIW I don't remember any user requesting something like this for tests, as documented - this would have to be a very advanced/elaborate scenario. Even we've managed fine without it.)