ruby on rails - SQLite3::SQLException while trying to set foreign keys? -

ruby on rails - SQLite3::SQLException while trying to set foreign keys? -

i have 3 models: user, micropost, , comment. i'm trying set foreign keys follows:

class createcomments < activerecord::migration def alter create_table :comments |t| t.text :content t.timestamps end add_index :comments, :micropost_id, :user_id end end

but error:

an error has occurred, , later migrations canceled:

sqlite3::sqlexception: near "user_id": syntax error: create user_id index "index_comments_on_micropost_id" on "comments" ("micropost_id")

i understand rails insert foreign keys based on belongs_to , has_many declarations in models. have set:

comment.rb:

class comment < activerecord::base belongs_to :micropost belongs_to :user end

micropost.rb:

class micropost < activerecord::base attr_accessible :title, :content belongs_to :user has_many :comments end

user.rb:

class user < activerecord::base # include default devise modules. others available are: # :token_authenticatable, :encryptable, :confirmable, :lockable, :timeoutable , :omniauthable devise :database_authenticatable, :registerable, :recoverable, :rememberable, :trackable, :validatable # setup accessible (or protected) attributes model attr_accessible :email, :password, :password_confirmation, :remember_me has_many :microposts has_many :comments end

any suggestions prepare this?

if want create index on 2 columns, syntax add_index table_name, [column1_name, column2_name], options. need define columns in table (activerecord not add together them automatically when add together belongs_to in model class). migration should be

class createcomments < activerecord::migration def alter create_table :comments |t| t.text :content t.integer :micropost_id t.integer :user_id t.timestamps end add_index :comments, [:micropost_id, :user_id] end end

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