Migrating To Microsoft Data Sqlclient

System.Data.SqlClient to Microsoft.Data.SqlClient Migration

Overview

Migrate .NET projects from System.Data.SqlClient to Microsoft.Data.SqlClient, covering package references, code files, connection string validation, and configuration changes. The migration includes documenting behavioral differences that require runtime verification.

Scope Determination

• Single project specified → migrate that project only
• Solution specified → migrate all projects referencing System.Data.SqlClient
• Scope unclear → ask the user

NuGet package names and assembly names are case-insensitive. Account for this when searching for or removing dependencies to avoid missed references.

Workflow

Complete all steps without pausing between them. Each step builds on the previous one, and partial migration leaves the codebase in a broken state.

Migration Progress:
- [ ] Step 1: Update package dependencies
- [ ] Step 2: Update code files
- [ ] Step 3: Validate migration (repeat Steps 2-3 until clean)
- [ ] Step 4: Build verification
- [ ] Step 5: Connection string validation

Step 1: Update Package Dependencies

For each project with an explicit dependency on System.Data.SqlClient in the project file or imported MSBuild targets (skip projects receiving it transitively — adding a new direct reference would create unnecessary coupling):

• Remove the System.Data.SqlClient package reference and assembly reference
• Add Microsoft.Data.SqlClient with a version supporting the project's target framework. Use available tools to determine the best version; fall back to manual determination only if no tool is available
• Central Package Management (CPM): Also remove System.Data.SqlClient from Directory.Packages.props. Add Microsoft.Data.SqlClient as a PackageVersion element in Directory.Packages.props and a version-less PackageReference in the project file

Step 2: Update Code Files

Search the affected projects and projects that depend on them (transitive consumers may reference System.Data.SqlClient types). Use search tools and pass root folders for all relevant projects.

• Replace System.Data.SqlClient usages with Microsoft.Data.SqlClient equivalents. Preserve all business logic — never insert placeholders
• Check for using statements, types, and API from the System.Data.SqlClient namespace (skip comments and string literal constants)
• For using statements: if other System.Data.SqlClient API usage remains in the file, replace the using; if no other usage exists, remove the using instead of replacing it. Do not add Microsoft.Data.SqlClient usings to files that had no System.Data.SqlClient usings
• Track any code that cannot be converted or has potential runtime behavior changes — flag these for the user

Step 3: Validate Migration

Search for System.Data.SqlClient across all affected projects and their dependents. If any references remain, return to Step 2. Repeat until no System.Data.SqlClient references exist.

Step 4: Build Verification

Build all modified projects. Fix all build errors before proceeding — a partial fix leaves the codebase unusable.

Step 5: Connection String Validation

Search for connection strings in app.config, web.config, and appsettings.json across affected projects and dependents. For connection strings pointing to databases:

• If Encrypt or TrustServerCertificate are not explicitly set, flag for the user — defaults changed (see Key Behavioral Differences below)
• If Encrypt is a bool value and the target is Microsoft.Data.SqlClient v5.0+, convert it to the corresponding SqlConnectionEncryptOption enum value and flag for user validation

Key Behavioral Differences

These differences cause silent runtime behavior changes. Flag them in the migration report.

Encrypt Property Changes

• System.Data.SqlClient: Encrypt defaults to false
• Microsoft.Data.SqlClient v4.0+: Encrypt defaults to true
• Microsoft.Data.SqlClient v5.0+: Encrypt is a SqlConnectionEncryptOption enum (Optional, Mandatory, Strict), no longer a bool

TrustServerCertificate

• In System.Data.SqlClient, server certificates were only validated when Encrypt was true
• In Microsoft.Data.SqlClient v4.0+, the driver always validates the server certificate based on TrustServerCertificate
• Self-signed certificates require TrustServerCertificate=true

DateTime Behavior

• DbType.Time: System.Data.SqlClient accepts DateTime; Microsoft.Data.SqlClient requires TimeSpan
• DbType.Date: System.Data.SqlClient sends date and time; Microsoft.Data.SqlClient truncates time components

Namespace Mappings (v5.0+)

Success Criteria

• No System.Data.SqlClient references remain in affected projects
• All modified projects build without errors
• Connection strings reviewed and documented for encryption default changes
• Any unconvertible patterns or behavioral changes flagged for the user