diff --git a/app b/app
deleted file mode 100755
index 4a0a09c..0000000
Binary files a/app and /dev/null differ
diff --git a/cmd/api/main.go b/cmd/api/main.go
index f56f25e..e2ef6ee 100644
--- a/cmd/api/main.go
+++ b/cmd/api/main.go
@@ -8,6 +8,7 @@ import (
 	"github.com/jackc/pgx/v5"
 
 	"tutorial.sqlc.dev/app/internal/author"
+	"tutorial.sqlc.dev/app/internal/db"
 )
 
 func run() error {
@@ -19,8 +20,9 @@ func run() error {
 	}
 	defer conn.Close(ctx)
 
+	querier := db.New(conn)
 	r := gin.Default()
-	authorCtl := author.NewController(conn)
+	authorCtl := author.NewController(querier)
 	author.Register(r, &authorCtl)
 
 	r.Run(":8000")
diff --git a/internal/author/query.sql b/db/query.sql
similarity index 100%
rename from internal/author/query.sql
rename to db/query.sql
diff --git a/internal/author/schema.sql b/db/schema.sql
similarity index 100%
rename from internal/author/schema.sql
rename to db/schema.sql
diff --git a/internal/author/controller.go b/internal/author/controller.go
index 0333f9a..86b12f8 100644
--- a/internal/author/controller.go
+++ b/internal/author/controller.go
@@ -4,26 +4,26 @@ import (
 	"strconv"
 
 	"github.com/gin-gonic/gin"
-	"tutorial.sqlc.dev/app/internal/author/gen"
+	"tutorial.sqlc.dev/app/internal/db"
 )
 
 type Controller struct {
-	queries gen.Queries
+	q db.Querier
 }
 
-func NewController(conn gen.DBTX) Controller {
+func NewController(queries db.Querier) Controller {
 	return Controller{
-		queries: *gen.New(conn),
+		q: queries,
 	}
 }
 
 func (u *Controller) ListAuthors(c *gin.Context) {
-	authors, err := u.queries.ListAuthors(c.Request.Context())
+	authors, err := u.q.ListAuthors(c.Request.Context())
 	if err != nil {
 		c.AbortWithError(500, err)
 		return
 	}
-	c.JSON(200, toAuthorSlice(authors))
+	c.JSON(200, authors)
 }
 
 func (u *Controller) GetAuthorByID(c *gin.Context) {
@@ -33,11 +33,11 @@ func (u *Controller) GetAuthorByID(c *gin.Context) {
 		c.AbortWithError(400, err)
 		return
 	}
-	author, err := u.queries.GetAuthor(c.Request.Context(), int64(id))
+	author, err := u.q.GetAuthor(c.Request.Context(), int64(id))
 	if err != nil {
 		c.JSON(400, gin.H{"message": "Author not found"})
 		return
 	}
 
-	c.JSON(200, toAuthor(author))
+	c.JSON(200, author)
 }
diff --git a/internal/author/gen/models.go b/internal/author/gen/models.go
deleted file mode 100644
index b8bcbb3..0000000
--- a/internal/author/gen/models.go
+++ /dev/null
@@ -1,15 +0,0 @@
-// Code generated by sqlc. DO NOT EDIT.
-// versions:
-//   sqlc v1.29.0
-
-package gen
-
-import (
-	"github.com/jackc/pgx/v5/pgtype"
-)
-
-type Author struct {
-	ID   int64
-	Name string
-	Bio  pgtype.Text
-}
diff --git a/internal/author/mapper.go b/internal/author/mapper.go
index 83c7fc4..9a99912 100644
--- a/internal/author/mapper.go
+++ b/internal/author/mapper.go
@@ -1,10 +1,12 @@
 package author
 
-import "tutorial.sqlc.dev/app/internal/author/gen"
+import (
+	"tutorial.sqlc.dev/app/internal/db"
+)
 
-func toAuthor(a gen.Author) Author {
+func toAuthor(a db.Author) Author {
 	return Author{
-		a.ID, a.Name, a.Bio.String,
+		a.ID, a.Name, a.Bio,
 	}
 }
 
diff --git a/internal/author/model.go b/internal/author/model.go
index d579ede..6e8f4ca 100644
--- a/internal/author/model.go
+++ b/internal/author/model.go
@@ -1,7 +1,7 @@
 package author
 
 type Author struct {
-	ID   int64  `json:"id"`
-	Name string `json:"name"`
-	Bio  string `json:"bio"`
+	ID   int64   `json:"id"`
+	Name string  `json:"name"`
+	Bio  *string `json:"bio"`
 }
diff --git a/internal/author/gen/db.go b/internal/db/db.go
similarity index 97%
rename from internal/author/gen/db.go
rename to internal/db/db.go
index 5017afe..0e4c3f4 100644
--- a/internal/author/gen/db.go
+++ b/internal/db/db.go
@@ -2,7 +2,7 @@
 // versions:
 //   sqlc v1.29.0
 
-package gen
+package db
 
 import (
 	"context"
diff --git a/internal/db/models.go b/internal/db/models.go
new file mode 100644
index 0000000..c90a57f
--- /dev/null
+++ b/internal/db/models.go
@@ -0,0 +1,11 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.29.0
+
+package db
+
+type Author struct {
+	ID   int64   `json:"id"`
+	Name string  `json:"name"`
+	Bio  *string `json:"bio"`
+}
diff --git a/internal/db/querier.go b/internal/db/querier.go
new file mode 100644
index 0000000..b569be0
--- /dev/null
+++ b/internal/db/querier.go
@@ -0,0 +1,19 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.29.0
+
+package db
+
+import (
+	"context"
+)
+
+type Querier interface {
+	CreateAuthor(ctx context.Context, arg CreateAuthorParams) (Author, error)
+	DeleteAuthor(ctx context.Context, id int64) error
+	GetAuthor(ctx context.Context, id int64) (Author, error)
+	ListAuthors(ctx context.Context) ([]Author, error)
+	UpdateAuthor(ctx context.Context, arg UpdateAuthorParams) error
+}
+
+var _ Querier = (*Queries)(nil)
diff --git a/internal/author/gen/query.sql.go b/internal/db/query.sql.go
similarity index 92%
rename from internal/author/gen/query.sql.go
rename to internal/db/query.sql.go
index 5d04ce3..0221067 100644
--- a/internal/author/gen/query.sql.go
+++ b/internal/db/query.sql.go
@@ -3,12 +3,10 @@
 //   sqlc v1.29.0
 // source: query.sql
 
-package gen
+package db
 
 import (
 	"context"
-
-	"github.com/jackc/pgx/v5/pgtype"
 )
 
 const createAuthor = `-- name: CreateAuthor :one
@@ -21,8 +19,8 @@ RETURNING id, name, bio
 `
 
 type CreateAuthorParams struct {
-	Name string
-	Bio  pgtype.Text
+	Name string  `json:"name"`
+	Bio  *string `json:"bio"`
 }
 
 func (q *Queries) CreateAuthor(ctx context.Context, arg CreateAuthorParams) (Author, error) {
@@ -88,9 +86,9 @@ RETURNING id, name, bio
 `
 
 type UpdateAuthorParams struct {
-	ID   int64
-	Name string
-	Bio  pgtype.Text
+	ID   int64   `json:"id"`
+	Name string  `json:"name"`
+	Bio  *string `json:"bio"`
 }
 
 func (q *Queries) UpdateAuthor(ctx context.Context, arg UpdateAuthorParams) error {
diff --git a/sqlc.yaml b/sqlc.yaml
index cc12fba..5c35d2e 100644
--- a/sqlc.yaml
+++ b/sqlc.yaml
@@ -1,10 +1,13 @@
 version: "2"
 sql:
   - engine: "postgresql"
-    queries: "internal/author/query.sql"
-    schema: "internal/author/schema.sql"
+    queries: "db/query.sql"
+    schema: "db/schema.sql"
     gen:
       go:
-        package: "gen"
-        out: "internal/author/gen"
+        package: "db"
+        out: "internal/db"
         sql_package: "pgx/v5"
+        emit_json_tags: true
+        emit_interface: true
+        emit_pointers_for_null_types: true
diff --git a/tutorial/db.go b/tutorial/db.go
deleted file mode 100644
index 5f69f0f..0000000
--- a/tutorial/db.go
+++ /dev/null
@@ -1,32 +0,0 @@
-// Code generated by sqlc. DO NOT EDIT.
-// versions:
-//   sqlc v1.29.0
-
-package tutorial
-
-import (
-	"context"
-
-	"github.com/jackc/pgx/v5"
-	"github.com/jackc/pgx/v5/pgconn"
-)
-
-type DBTX interface {
-	Exec(context.Context, string, ...interface{}) (pgconn.CommandTag, error)
-	Query(context.Context, string, ...interface{}) (pgx.Rows, error)
-	QueryRow(context.Context, string, ...interface{}) pgx.Row
-}
-
-func New(db DBTX) *Queries {
-	return &Queries{db: db}
-}
-
-type Queries struct {
-	db DBTX
-}
-
-func (q *Queries) WithTx(tx pgx.Tx) *Queries {
-	return &Queries{
-		db: tx,
-	}
-}
diff --git a/tutorial/models.go b/tutorial/models.go
deleted file mode 100644
index bac90c3..0000000
--- a/tutorial/models.go
+++ /dev/null
@@ -1,15 +0,0 @@
-// Code generated by sqlc. DO NOT EDIT.
-// versions:
-//   sqlc v1.29.0
-
-package tutorial
-
-import (
-	"github.com/jackc/pgx/v5/pgtype"
-)
-
-type Author struct {
-	ID   int64
-	Name string
-	Bio  pgtype.Text
-}