Strategy for Dynamic Tags in MongoDB

On Facebook statues, you can start typing an @ and tag a user in a status. This question is not about the frontend, but rather how to store the data for that feature. What is the best way to achieve this functionality in a generic way for representing any mongodb entity in a string in a dynamic way. The goal being if the entity changes, it representation in the stored string also changes. For example one idea I had was this:

Post: {
     _id: "48ajsdlfhsdjfkjsljsd"
     name: "Post One",
     text: "@user is the best for liking @thing, and @thing"
     tags: [user:1234, thing:456, thing:789]
 }
 

So I would load this post, then look at the tags, load the models for each tag type and id, then rewrite the string to be: "Chris is the best for liking StackOverflow, and Mongo". This seems inefficient, any better ideas?

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