feat: add YDB type annotations in struct field tags for runtime type validation

examples/.gitignore

@@ -1 +1 @@
-/.golangci.yml
+/.golangci.yml

examples/type_annotations/.gitignore

@@ -0,0 +1 @@
+type_annotations

examples/type_annotations/README.md

@@ -0,0 +1,78 @@
+# Type Annotations Example
+
+This example demonstrates how to use YDB type annotations in struct field tags to validate column types and improve code documentation.
+
+## Features Demonstrated
+
+1. **Basic Type Annotations**: Annotate struct fields with YDB types like `Uint64`, `Text`, `Double`
+2. **Complex Type Annotations**: Use `List<T>`, `Optional<T>`, and `Dict<K,V>` annotations
+3. **Type Validation**: Automatic validation that database column types match your struct annotations
+4. **Error Detection**: Clear error messages when types don't match
+
+## Struct Tag Syntax
+
+The type annotation is added to the struct tag using the `type:` prefix:
+
+```go
+type Product struct {
+    // Column name: product_id, YDB type: Uint64
+    ProductID uint64 `sql:"product_id,type:Uint64"`
+
+    // Column name: tags, YDB type: List<Text>
+    Tags []string `sql:"tags,type:List<Text>"`
+
+    // Column name: rating, YDB type: Optional<Double>
+    Rating *float64 `sql:"rating,type:Optional<Double>"`
+}
+```
+
+## Supported YDB Types
+
+### Primitive Types
+- `Bool`, `Int8`, `Int16`, `Int32`, `Int64`
+- `Uint8`, `Uint16`, `Uint32`, `Uint64`
+- `Float`, `Double`
+- `Date`, `Datetime`, `Timestamp`
+- `Text` (UTF-8), `Bytes` (binary)
+- `JSON`, `YSON`, `UUID`
+
+### Complex Types
+- `List<T>` - List of items of type T
+- `Optional<T>` - Optional (nullable) value of type T
+- `Dict<K,V>` - Dictionary with key type K and value type V
+
+### Nested Types
+You can nest complex types:
+- `List<Optional<Text>>` - List of optional text values
+- `Optional<List<Uint64>>` - Optional list of unsigned integers
+- `Dict<Text,List<Uint64>>` - Dictionary mapping text to lists of integers
+
+## Benefits
+
+1. **Documentation**: Type annotations serve as inline documentation of expected database schema
+2. **Validation**: Runtime validation ensures your Go types match the database schema
+3. **Error Prevention**: Catch type mismatches early before they cause runtime errors
+4. **Code Clarity**: Makes it explicit what YDB types you expect from the database
+
+## Running the Example
+
+```bash
+# Set your YDB connection string
+export YDB_CONNECTION_STRING="grpc://localhost:2136/local"
+
+# Run the example
+go run main.go
+```
+
+## When to Use Type Annotations
+
+Type annotations are **optional** but recommended when:
+
+- Working with complex types (Lists, Dicts, Optional values)
+- Building a strict API where type safety is critical
+- Documenting expected database schema in code
+- Working in a team where schema changes need to be validated
+
+## Backward Compatibility
+
+Type annotations are completely optional. Existing code without type annotations continues to work exactly as before. You can add annotations gradually to your codebase.

examples/type_annotations/main.go

@@ -0,0 +1,206 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"path"
+	"time"
+
+	environ "github.com/ydb-platform/ydb-go-sdk-auth-environ"
+	ydb "github.com/ydb-platform/ydb-go-sdk/v3"
+	"github.com/ydb-platform/ydb-go-sdk/v3/query"
+	"github.com/ydb-platform/ydb-go-sdk/v3/sugar"
+)
+
+var connectionString = flag.String("ydb", os.Getenv("YDB_CONNECTION_STRING"), "YDB connection string")
+
+func main() {
+	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel()
+
+	flag.Parse()
+
+	if *connectionString == "" {
+		log.Fatal("YDB_CONNECTION_STRING environment variable or -ydb flag must be set")
+	}
+
+	db, err := ydb.Open(ctx, *connectionString,
+		environ.WithEnvironCredentials(),
+	)
+	if err != nil {
+		log.Fatalf("failed to connect to YDB: %v", err)
+	}
+	defer func() { _ = db.Close(ctx) }()
+
+	prefix := path.Join(db.Name(), "type_annotations_example")
+
+	// Clean up any existing data
+	_ = sugar.RemoveRecursive(ctx, db, prefix)
+
+	// Create table
+	if err := createTable(ctx, db.Query(), prefix); err != nil {
+		log.Fatalf("failed to create table: %v", err)
+	}
+
+	// Insert data
+	if err := insertData(ctx, db.Query(), prefix); err != nil {
+		log.Fatalf("failed to insert data: %v", err)
+	}
+
+	// Read data with type annotations
+	if err := readDataWithTypeAnnotations(ctx, db.Query(), prefix); err != nil {
+		log.Fatalf("failed to read data: %v", err)
+	}
+
+	// Demonstrate type mismatch detection
+	if err := demonstrateTypeMismatch(ctx, db.Query(), prefix); err != nil {
+		log.Printf("Expected error (type mismatch): %v", err)
+	}
+
+	// Clean up
+	_ = sugar.RemoveRecursive(ctx, db, prefix)
+
+	fmt.Println("\nExample completed successfully!")
+}
+
+func createTable(ctx context.Context, c query.Client, prefix string) error {
+	return c.Exec(ctx, fmt.Sprintf(`
+		CREATE TABLE %s (
+			product_id Uint64,
+			name Text,
+			description Text,
+			price Uint64,
+			tags List<Text>,
+			rating Optional<Double>,
+			metadata Dict<Text, Text>,
+			PRIMARY KEY (product_id)
+		)`, "`"+path.Join(prefix, "products")+"`"),
+		query.WithTxControl(query.NoTx()),
+	)
+}
+
+func insertData(ctx context.Context, c query.Client, prefix string) error {
+	return c.Exec(ctx, fmt.Sprintf(`
+		INSERT INTO %s (product_id, name, description, price, tags, rating)
+		VALUES (
+			1,
+			"Laptop",
+			"High-performance laptop",
+			999,
+			["electronics", "computer", "portable"],
+			4.5
+		);
+	`, "`"+path.Join(prefix, "products")+"`"))
+}
+
+// Product demonstrates struct with YDB type annotations
+type Product struct {
+	// Basic types with annotations
+	ProductID   uint64  `sql:"product_id,type:Uint64"`
+	Name        string  `sql:"name,type:Text"`
+	Description string  `sql:"description,type:Text"`
+	Price       uint64  `sql:"price,type:Uint64"`
+
+	// List type annotation
+	Tags        []string `sql:"tags,type:List<Text>"`
+
+	// Optional type annotation (can be NULL)
+	Rating      *float64 `sql:"rating,type:Optional<Double>"`
+}
+
+func readDataWithTypeAnnotations(ctx context.Context, c query.Client, prefix string) error {
+	fmt.Println("\n=== Reading data with type annotations ===")
+
+	return c.Do(ctx, func(ctx context.Context, s query.Session) error {
+		result, err := s.Query(ctx, fmt.Sprintf(`
+			SELECT product_id, name, description, price, tags, rating
+			FROM %s
+		`, "`"+path.Join(prefix, "products")+"`"),
+			query.WithTxControl(query.TxControl(query.BeginTx(query.WithSnapshotReadOnly()))),
+		)
+		if err != nil {
+			return err
+		}
+		defer result.Close(ctx)
+
+		for rs, err := range result.ResultSets(ctx) {
+			if err != nil {
+				return err
+			}
+
+			for row, err := range rs.Rows(ctx) {
+				if err != nil {
+					return err
+				}
+
+				var product Product
+
+				// ScanStruct will validate that database column types match the annotations
+				if err := row.ScanStruct(&product); err != nil {
+					return fmt.Errorf("scan error: %w", err)
+				}
+
+				fmt.Printf("\nProduct ID: %d\n", product.ProductID)
+				fmt.Printf("Name: %s\n", product.Name)
+				fmt.Printf("Description: %s\n", product.Description)
+				fmt.Printf("Price: $%d\n", product.Price)
+				fmt.Printf("Tags: %v\n", product.Tags)
+				if product.Rating != nil {
+					fmt.Printf("Rating: %.1f/5.0\n", *product.Rating)
+				} else {
+					fmt.Println("Rating: Not rated")
+				}
+			}
+		}
+
+		return nil
+	})
+}
+
+// ProductWrongType demonstrates what happens when type annotations don't match
+type ProductWrongType struct {
+	ProductID uint64  `sql:"product_id,type:Text"` // Wrong! Should be Uint64
+	Name      string  `sql:"name,type:Text"`
+}
+
+func demonstrateTypeMismatch(ctx context.Context, c query.Client, prefix string) error {
+	fmt.Println("\n=== Demonstrating type mismatch detection ===")
+
+	return c.Do(ctx, func(ctx context.Context, s query.Session) error {
+		result, err := s.Query(ctx, fmt.Sprintf(`
+			SELECT product_id, name
+			FROM %s
+		`, "`"+path.Join(prefix, "products")+"`"),
+			query.WithTxControl(query.TxControl(query.BeginTx(query.WithSnapshotReadOnly()))),
+		)
+		if err != nil {
+			return err
+		}
+		defer result.Close(ctx)
+
+		for rs, err := range result.ResultSets(ctx) {
+			if err != nil {
+				return err
+			}
+
+			for row, err := range rs.Rows(ctx) {
+				if err != nil {
+					return err
+				}
+
+				var product ProductWrongType
+
+				// This will fail because product_id is Uint64 in the database
+				// but the annotation says it should be Text
+				if err := row.ScanStruct(&product); err != nil {
+					return fmt.Errorf("type mismatch detected: %w", err)
+				}
+			}
+		}
+
+		return nil
+	})
+}

internal/query/scanner/data.go

@@ -31,6 +31,16 @@ func (d Data) seekByName(name string) (value.Value, error) {
 	return nil, xerrors.WithStackTrace(fmt.Errorf("'%s': %w", name, ErrColumnsNotFoundInRow))
 }
 
+func (d Data) columnTypeByName(name string) (*Ydb.Type, error) {
+	for i := range d.columns {
+		if d.columns[i].GetName() == name {
+			return d.columns[i].GetType(), nil
+		}
+	}
+
+	return nil, xerrors.WithStackTrace(fmt.Errorf("'%s': %w", name, ErrColumnsNotFoundInRow))
+}
+
 func (d Data) seekByIndex(idx int) value.Value {
 	return value.FromYDB(d.columns[idx].GetType(), d.values[idx])
 }