Eloquent我可以在哪里提到模型关系？

I have models with appropriate belongsTo/hasMany relationships defined, and I want to query one table based on properties of a joined table. I can do it if I define the join in my query, but is there something I can do so that I don't have to define the join everytime I want to query a model on it's relation?

Forinstance. the following does not work, unless I define a join:

FileAssociation::with('file')->where('files.file_type_version_id', $file->file_type_version_id)->get()

I think what you want is Eager Load Constraints basically you can do this

FileAssociation::with(array('file' => function($query)
{
  $query->where('file_type_version_id',$file->file_type_version_id);
}))->get(); 

Check out the docs on Eager Loading

Edit

If you are using Laravel 4.1 now you have access to the whereHas() method if you want to return the FileAssociation only if there is at least one "file"

FileAssociation::whereHas('file' => function($query)
{
  $query->where('file_type_version_id',$file->file_type_version_id);
})->get(); 

Check out the docs on Quering Relations