Implementing Dapper Queries Skill for Claude

Repository Pattern

All Dapper implementations live in src/Infrastructure/Dapper/Repositories/. Each repository class implements an interface from src/Core/ and uses stored procedures for all database operations. The repository method is intentionally thin — it maps C# parameters to SQL parameters and maps result sets back to domain objects.

Stored procedures over inline SQL

The default pattern is stored procedures for all Dapper database operations. Some exceptions exist where inline SQL is used — these are provided automatically by the repository base class and parent patterns, not written ad-hoc in individual repository methods.

Workflow

• Define/update the stored procedure in src/Sql/dbo/Stored Procedures/ — use plain CREATE PROCEDURE (SSDT syntax)
• Create a migration script in util/Migrator/DbScripts/ that deploys it — use CREATE OR ALTER PROCEDURE (idempotent)
• Implement the repository method in src/Infrastructure/Dapper/Repositories/ using DapperServiceProvider to call the procedure
• Write integration tests using [DatabaseData] attribute

The stored procedure is the source of truth for MSSQL query behavior. The Dapper repository method is thin — it maps parameters and results.

Stored procedure naming convention

Procedures follow {Entity}_{Action} pattern: User_Create, Cipher_ReadManyByUserId, Organization_DeleteById. Tooling and code generation rely on this convention to map repository methods to their procedures.

Key Decisions That Trip Up AI Assistants

CREATE OR ALTER vs CREATE PROCEDURE — depends on file location

Bitwarden maintains two copies of every stored procedure in different contexts with different toolchain constraints:

| Context | Location | Required syntax |

| ---------------------- | -------------------------------- | --------------------------- |

| SSDT schema source | src/Sql/dbo/Stored Procedures/ | CREATE PROCEDURE (plain) |

| Migration script | util/Migrator/DbScripts/ | CREATE OR ALTER PROCEDURE |

Why they differ:

• SSDT projects do not support CREATE OR ALTER — using it produces build errors. SSDT manages object lifecycle through its own deployment model, so each source file must contain a bare CREATE PROCEDURE.
• Migration scripts must be idempotent because they may be re-run. CREATE OR ALTER works whether the procedure exists or not. Never use bare CREATE PROCEDURE in a migration.

SSDT table files require GO batch separators

In src/Sql/dbo/Tables/, SSDT requires a GO batch separator between CREATE TABLE and any subsequent CREATE INDEX or CREATE NONCLUSTERED INDEX statements.

-- CORRECT — GO separates DDL statements for SSDT
CREATE TABLE [dbo].[Example] (
    [Id] UNIQUEIDENTIFIER NOT NULL,
    [Name] NVARCHAR(256) NOT NULL,
    CONSTRAINT [PK_Example] PRIMARY KEY CLUSTERED ([Id] ASC)
)
GO

CREATE NONCLUSTERED INDEX [IX_Example_Name]
    ON [dbo].[Example] ([Name] ASC)
GO

New parameters must be nullable with defaults

When adding parameters to existing stored procedures, always use @NewParam DATATYPE = NULL. Existing callers don't pass the new parameter — without a default, they break.

NOT NULL columns: use inline defaults, not ALTER-UPDATE-ALTER

Adding a NOT NULL column by first adding it nullable, updating all rows, then altering to NOT NULL causes a full table scan. Instead, use ADD [Column] INT NOT NULL CONSTRAINT DF_Table_Column DEFAULT 0 — this is a metadata-only operation in SQL Server. This is the single most common mistake AI assistants make with Bitwarden migrations.

Never create indexes on large tables in migration scripts

Creating indexes on dbo.Cipher, dbo.OrganizationUser, or other large tables in migration scripts can cause outages. Never specify ONLINE = ON in scripts — production handles this automatically, and the option fails on unsupported SQL Server editions. Large index operations belong in DbScripts_manual.

Use defaults only for numeric types

Use defaults for BIT, TINYINT, INT, BIGINT. Never use defaults for VARCHAR, NVARCHAR, or MAX types. SQL Server handles these differently and defaults on strings create unexpected behavior with EF Core migrations.

Views require metadata refresh

After modifying a table, any views that reference it have stale metadata. Call sp_refreshview on affected views. After altering views, call sp_refreshsqlmodule on dependent procedures. This is the most frequently forgotten step.

GUID columns use UNIQUEIDENTIFIER

All entity IDs are UNIQUEIDENTIFIER populated by CoreHelpers.GenerateComb() in application code, not by SQL Server. Never use NEWID() or NEWSEQUENTIALID() in stored procedures.

EF Parity Requirement

Every stored procedure's behavior must be exactly replicated in the EF Core implementation. When writing a new stored procedure, think about how the EF implementation will reproduce the same filtering, ordering, and side effects. If a stored procedure does something complex (e.g., conditional updates, multi-table operations), document the expected behavior clearly so the EF implementation can match it.

Critical Rules

These are the most frequently violated conventions. Claude cannot fetch the linked docs at runtime, so these are inlined here:

• SET NOCOUNT ON at the start of every stored procedure
• Parameter naming: @ParamName in PascalCase, matching C# property names
• Migration scripts must be idempotent — use CREATE OR ALTER in util/Migrator/DbScripts/; use plain CREATE PROCEDURE in SSDT source (src/Sql/dbo/)
• Constraint naming: PK_TableName, FK_Child_Parent, IX_Table_Column, DF_Table_Column
• Stored procedure file naming: one procedure per file, named {Entity}_{Action}.sql

Examples

Stored procedure creation — SSDT source vs migration script

-- SSDT source file: src/Sql/dbo/Stored Procedures/User_ReadById.sql
-- Use plain CREATE PROCEDURE (SSDT does not support CREATE OR ALTER)
CREATE PROCEDURE [dbo].[User_ReadById]
    @Id UNIQUEIDENTIFIER
AS
BEGIN
    SET NOCOUNT ON
    SELECT * FROM [dbo].[User] WHERE [Id] = @Id
END

-- Migration script: util/Migrator/DbScripts/YYYY-MM-DD_00_AddUser_ReadById.sql
-- Use CREATE OR ALTER for idempotency
CREATE OR ALTER PROCEDURE [dbo].[User_ReadById]
    @Id UNIQUEIDENTIFIER
AS
BEGIN
    SET NOCOUNT ON
    SELECT * FROM [dbo].[User] WHERE [Id] = @Id
END

Adding a NOT NULL column

-- CORRECT — metadata-only operation, no table scan
ALTER TABLE [dbo].[Organization]
    ADD [UseCustomPermissions] BIT NOT NULL CONSTRAINT DF_Organization_UseCustomPermissions DEFAULT 0

-- WRONG — causes full table scan on large tables
ALTER TABLE [dbo].[Organization] ADD [UseCustomPermissions] BIT NULL
UPDATE [dbo].[Organization] SET [UseCustomPermissions] = 0
ALTER TABLE [dbo].[Organization] ALTER COLUMN [UseCustomPermissions] BIT NOT NULL

Adding parameters to existing procedures

-- CORRECT — existing callers won't break
CREATE OR ALTER PROCEDURE [dbo].[Cipher_Create]
    @Id UNIQUEIDENTIFIER,
    @NewField NVARCHAR(MAX) = NULL  -- default protects existing callers

-- WRONG — breaks all existing callers immediately
CREATE OR ALTER PROCEDURE [dbo].[Cipher_Create]
    @Id UNIQUEIDENTIFIER,
    @NewField NVARCHAR(MAX)  -- no default = required parameter

Further Reading

• SQL code style
• Database migrations (MSSQL)