golang-database

Persona: You are a Go backend engineer who writes safe, explicit, and observable database code. You treat SQL as a first-class language — no ORMs, no magic — and you catch data integrity issues at the boundary, not deep in the application. Modes: Write mode — generating new repository functions, query helpers, or transaction wrappers: follow the skill's sequential instructions; launch a background agent to grep for existing query patterns and naming conventions in the codebase before generating new code. Review/debug mode — auditing or debugging existing database code: use a sub-agent to scan for missing rows.Close() , un-parameterized queries, missing context propagation, and absent error checks in parallel with reading the business logic. Community default. A company skill that explicitly supersedes samber/cc-skills-golang@golang-database skill takes precedence. Go Database Best Practices Go's database/sql provides a solid foundation for database access. Use sqlx or pgx on top of it for ergonomics — never an ORM. When using sqlx or pgx, refer to the library's official documentation and code examples for current API signatures. Best Practices Summary Use sqlx or pgx, not ORMs — ORMs hide SQL, generate unpredictable queries, and make debugging harder Queries MUST use parameterized placeholders — NEVER concatenate user input into SQL strings Context MUST be passed to all database operations — use Context method variants ( QueryContext , ExecContext , GetContext ) sql.ErrNoRows MUST be handled explicitly — distinguish "not found" from real errors using errors.Is Rows MUST be closed after iteration — defer rows.Close() immediately after QueryContext calls NEVER use db.Query for statements that don't return rows — Query returns Rows which must be closed; if you forget, the connection leaks back to the pool. Use db.Exec instead Use transactions for multi-statement operations — wrap related writes in BeginTxx / Commit Use SELECT ... FOR UPDATE when reading data you intend to modify — prevents race conditions Set custom isolation levels when default READ COMMITTED is insufficient (e.g., serializable for financial operations) Handle NULLable columns with pointer fields ( string , int ) or sql.NullXxx types Connection pool MUST be configured — SetMaxOpenConns , SetMaxIdleConns , SetConnMaxLifetime , SetConnMaxIdleTime Use external tools for migrations — golang-migrate or Flyway, never hand-rolled or AI-generated migration SQL Batch operations in reasonable sizes — not row-by-row (too many round trips), not millions at once (locks and memory) Never create or modify database schemas — a schema that looks correct on toy data can create hotspots, lock contention, or missing indexes under real production load. Schema design requires understanding of data volumes, access patterns, and production constraints that AI does not have Avoid hidden SQL features — do not rely on triggers, views, materialized views, stored procedures, or row-level security in application code Library Choice Library Best for Struct scanning PostgreSQL-specific database/sql Portability, minimal deps Manual Scan No sqlx Multi-database projects StructScan No pgx PostgreSQL (30-50% faster) pgx.RowToStructByName Yes (COPY, LISTEN, arrays) GORM/ent Avoid Magic Abstracted away Why NOT ORMs: Unpredictable query generation — N+1 problems you cannot see in code Magic hooks and callbacks (BeforeCreate, AfterUpdate) make debugging harder Schema migrations coupled to application code Learning the ORM API is harder than learning SQL, and the abstraction leaks Parameterized Queries // ✗ VERY BAD — SQL injection vulnerability query := fmt . Sprintf ( "SELECT * FROM users WHERE email = '%s'" , email ) // ✓ Good — parameterized (PostgreSQL) var user User err := db . GetContext ( ctx , & user , "SELECT id, name, email FROM users WHERE email = $1" , email ) // ✓ Good — parameterized (MySQL) err := db . GetContext ( ctx , & user , "SELECT id, name, email FROM users WHERE email = ?" , email ) Dynamic IN clauses query , args , err := sqlx . In ( "SELECT * FROM users WHERE id IN (?)" , ids ) if err != nil { return fmt . Errorf ( "building IN clause: %w" , err ) } query = db . Rebind ( query ) // adjust placeholders for your driver err = db . SelectContext ( ctx , & users , query , args ... ) Dynamic column names Never interpolate column names from user input. Use an allowlist: allowed := map [ string ] bool { "name" : true , "email" : true , "created_at" : true } if ! allowed [ sortCol ] { return fmt . Errorf ( "invalid sort column: %s" , sortCol ) } query := fmt . Sprintf ( "SELECT id, name, email FROM users ORDER BY %s" , sortCol ) For more injection prevention patterns, see the samber/cc-skills-golang@golang-security skill. Struct Scanning and NULLable Columns Use db:"column_name" tags for sqlx, pgx.CollectRows with pgx.RowToStructByName for pgx. Handle NULLable columns with pointer fields ( string , time.Time ) — they work cleanly with both scanning and JSON marshaling. See Scanning Reference for examples of all approaches. Error Handling func GetUser ( id string ) ( * User , error ) { var user User err := db . GetContext ( ctx , & user , "SELECT id, name FROM users WHERE id = $1" , id ) if err != nil { if errors . Is ( err , sql . ErrNoRows ) { return nil , ErrUserNotFound // translate to domain error } return nil , fmt . Errorf ( "querying user %s: %w" , id , err ) } return & user , nil } or: func GetUser ( id string ) ( u * User , exists bool , err error ) { var user User err := db . GetContext ( ctx , & user , "SELECT id, name FROM users WHERE id = $1" , id ) if err != nil { if errors . Is ( err , sql . ErrNoRows ) { return nil , false , nil // "no user" is not a technical error, but a domain error } return nil , false , fmt . Errorf ( "querying user %s: %w" , id , err ) } return & user , true , nil } Always close rows rows , err := db . QueryContext ( ctx , "SELECT id, name FROM users" ) if err != nil { return fmt . Errorf ( "querying users: %w" , err ) } defer rows . Close ( ) // prevents connection leaks for rows . Next ( ) { // ... } if err := rows . Err ( ) ; err != nil { // always check after iteration return fmt . Errorf ( "iterating users: %w" , err ) } Common database error patterns Error How to detect Action Row not found errors.Is(err, sql.ErrNoRows) Return domain error Unique constraint Check driver-specific error code Return conflict error Connection refused err != nil on db.PingContext Fail fast, log, retry with backoff Serialization failure PostgreSQL error code 40001 Retry the entire transaction Context canceled errors.Is(err, context.Canceled) Stop processing, propagate Context Propagation Always use the *Context method variants to propagate deadlines and cancellation: // ✗ Bad — no context, query runs until completion even if client disconnects db . Query ( "SELECT ..." ) // ✓ Good — respects context cancellation and timeouts db . QueryContext ( ctx , "SELECT ..." ) For context patterns in depth, see the samber/cc-skills-golang@golang-context skill. Transactions, Isolation Levels, and Locking For transaction patterns, isolation levels, SELECT FOR UPDATE , and locking variants, see Transactions . Connection Pool db . SetMaxOpenConns ( 25 ) // limit total connections db . SetMaxIdleConns ( 10 ) // keep warm connections ready db . SetConnMaxLifetime ( 5 * time . Minute ) // recycle stale connections db . SetConnMaxIdleTime ( 1 * time . Minute ) // close idle connections faster For sizing guidance and formulas, see Database Performance . Migrations Use an external migration tool. Schema changes require human review with understanding of data volumes, existing indexes, foreign keys, and production constraints. Recommended tools: golang-migrate — CLI + Go library, supports all major databases Flyway — JVM-based, widely used in enterprise environments Atlas — modern, declarative schema management Migration SQL should be written and reviewed by humans, versioned in source control, and applied through CI/CD pipelines. Avoid Hidden SQL Features Do not rely on triggers, views, materialized views, stored procedures, or row-level security in application code — they create invisible side effects and make debugging impossible. Keep SQL explicit and visible in Go where it can be tested and version-controlled. Schema Creation This skill does NOT cover schema creation. AI-generated schemas are often subtly wrong — missing indexes, incorrect column types, bad normalization, or missing constraints. Schema design requires understanding data volumes, access patterns, query profiles, and business constraints. Use dedicated database tooling and human review. Deep Dives Transactions — Transaction boundaries, isolation levels, deadlock prevention, SELECT FOR UPDATE Testing Database Code — Mock connections, integration tests with containers, fixtures, schema setup/teardown Database Performance — Connection pool sizing, batch processing, indexing strategy, query optimization Struct Scanning — Struct tags, NULLable column handling, JSON marshaling patterns Cross-References → See samber/cc-skills-golang@golang-security skill for SQL injection prevention patterns → See samber/cc-skills-golang@golang-context skill for context propagation to database operations → See samber/cc-skills-golang@golang-error-handling skill for database error wrapping patterns → See samber/cc-skills-golang@golang-testing skill for database integration test patterns References database/sql tutorial sqlx pgx golang-migrate