Add solution for gorm challenge-2-associations (#853)

Co-authored-by: go-interview-practice-bot[bot] <230190823+go-interview-practice-bot[bot]@users.noreply.github.com>

Author: aswinsreeraj

packages/gorm/challenge-2-associations/submissions/aswinsreeraj/solution.go

@@ -0,0 +1,117 @@
+package main
+
+import (
+	"time"
+
+	"gorm.io/gorm"
+	"gorm.io/driver/sqlite"
+)
+
+// User represents a user in the blog system
+type User struct {
+	ID        uint   `gorm:"primaryKey"`
+	Name      string `gorm:"not null"`
+	Email     string `gorm:"unique;not null"`
+	Posts     []Post `gorm:"foreignKey:UserID"`
+	CreatedAt time.Time
+	UpdatedAt time.Time
+}
+
+// Post represents a blog post
+type Post struct {
+	ID        uint   `gorm:"primaryKey"`
+	Title     string `gorm:"not null"`
+	Content   string `gorm:"type:text"`
+	UserID    uint   `gorm:"not null"`
+	User      User   `gorm:"foreignKey:UserID"`
+	Tags      []Tag  `gorm:"many2many:post_tags;"`
+	CreatedAt time.Time
+	UpdatedAt time.Time
+}
+
+// Tag represents a tag for categorizing posts
+type Tag struct {
+	ID    uint   `gorm:"primaryKey"`
+	Name  string `gorm:"unique;not null"`
+	Posts []Post `gorm:"many2many:post_tags;"`
+}
+
+// ConnectDB establishes a connection to the SQLite database and auto-migrates the models
+func ConnectDB() (*gorm.DB, error) {
+	// TODO: Implement database connection with auto-migration
+	db, err := gorm.Open(sqlite.Open("test.db"), &gorm.Config{})
+	if err != nil {
+	    return nil, err
+	}
+	err = db.AutoMigrate(&User{}, &Post{}, &Tag{})
+	return db, err
+}
+
+// CreateUserWithPosts creates a new user with associated posts
+func CreateUserWithPosts(db *gorm.DB, user *User) error {
+	// TODO: Implement user creation with posts
+	result := db.Create(user)
+	return result.Error
+}
+
+// GetUserWithPosts retrieves a user with all their posts preloaded
+func GetUserWithPosts(db *gorm.DB, userID uint) (*User, error) {
+	// TODO: Implement user retrieval with posts
+	var user User
+	result := db.Preload("Posts").First(&user, userID)
+	return &user, result.Error
+}
+
+// CreatePostWithTags creates a new post with specified tags
+func CreatePostWithTags(db *gorm.DB, post *Post, tagNames []string) error {
+	// TODO: Implement post creation with tags
+	if err := db.Create(post).Error; err != nil {
+	    return err
+	}
+	for _, name := range tagNames {
+	    var tag Tag
+	    db.FirstOrCreate(&tag, Tag{Name: name})
+	    db.Model(post).Association("Tags").Append(&tag)
+	}
+	return nil
+}
+
+// GetPostsByTag retrieves all posts that have a specific tag
+func GetPostsByTag(db *gorm.DB, tagName string) ([]Post, error) {
+	// TODO: Implement posts retrieval by tag
+	var posts []Post
+	err := db.Joins("JOIN post_tags ON posts.id = post_tags.post_id").
+	            Joins("JOIN tags ON post_tags.tag_id = tags.id").
+	            Where("tags.name = ?", tagName).
+	            Find(&posts).Error
+	return posts, err
+}
+
+// AddTagsToPost adds tags to an existing post
+func AddTagsToPost(db *gorm.DB, postID uint, tagNames []string) error {
+	// TODO: Implement adding tags to existing post
+	var post Post
+	result := db.First(&post, postID)
+	if result.Error != nil {
+	    return result.Error
+	}
+	for _, tagName := range tagNames {
+	    var tag Tag
+	    db.FirstOrCreate(&tag, Tag{Name: tagName})
+	    if err := db.Model(&post).Association("Tags").Append(&tag); err != nil {
+	     return err
+	 }   
+	}
+	return nil
+}
+
+// GetPostWithUserAndTags retrieves a post with user and tags preloaded
+func GetPostWithUserAndTags(db *gorm.DB, postID uint) (*Post, error) {
+	// TODO: Implement post retrieval with user and tags
+	var post Post
+	err := db.Preload("User").Preload("Tags").First(&post, postID).Error
+	if err != nil {
+	    return nil, err
+	}
+	return &post, nil
+}