How can I update/insert Object into inner List in Mongodb?

Question

Blog {
   id:"001"
   title:"This is a test blog",
   content:"...."
   comments:[{title:"comment1",content:".."},{title:"comment2",content:"..."}]    
}

comments is a inner list in blog.

But how can I retrieve only comment1? and How can I insert/update a new comment into the blog?if I get a full blog and insert/update the content into comments List,then save the full blog,how to solve concurrent isuue?

Thanks.

Answer 1

Blog {  
    id:"001"  
    title:"This is a test blog",  
    content:"...."  
    comments:[{title:"comment1",content:".."},{title:"comment2",content:"..."}]      
}

To insert new comment, use $push:

db.blogs.update({id:"001"}, {$push:{comments:{title:"commentX",content:".."}}});  

To update a comment, use $set:

db.blogs.update({id:"001"}, {$set :{"comments.2": {...} }});  
db.blogs.update({id:"001"}, {$set :{"comments.2.title": "new title" }});  

2 is the index of the given comment. Usage of quote mark is necessary.

Answer 2

To fetch the embedded document you need fetch the master document and search on his comments embedded document the document you want. There are no way to do better in MongoDB actually.

To insert/update in a embedded document you can use the $push and $set query system to do that.