Mongomapper嵌入文檔「無法序列化對象」錯誤

Question

我是很新的MongoDB和我使用西納特拉和mongomapper與以下設置更新嵌入文檔的值：

class TeamMember 
    include MongoMapper::Document 

    key :name, String, :required => true 

    many :team_member_projects 
end 

class TeamMemberProject 
    include MongoMapper::EmbeddedDocument 

    key :date, Date, :required => true 

    one :project 
end 

class Project 
    include MongoMapper::Document 

    key :name, String, :required => true 
end 

的修改代碼：

team_member = TeamMember.find(params[:team_member]) 
project = Project.find(params[:project]) 
date = Date.parse(params[:date]) 

tm_project = TeamMemberProject.new(:project => project, :date => date) 
team_member.push(:team_member_projects => tm_project) 
team_member.save 

，但我得到的錯誤.push行：

BSON::InvalidDocument at /project/add 
Cannot serialize an object of class TeamMemberProject into BSON. 

我沒有正確聲明我的嵌入式文檔嗎？或者還有另一種更新嵌入式文檔的方式，我不知道。我試圖使用方法：http://mongomapper.com/documentation/plugins/modifiers.html#push

Answer 1

這似乎是工作

team_member = TeamMember.find(params[:team_member]) 
project = Project.find(params[:project]) 
date = Date.parse(params[:date]) 

tm_project = TeamMemberProject.new(:project_id => project.id, :date => date) 
team_member.team_member_projects << tm_project 
team_member.save 

好像我不得不使用project.id。不知道爲什麼。也不知道爲什麼我的.push不起作用，因爲我會認爲它的作用與<<一樣。