集合中每个文档的 MongoDB : how to set a new field equal to the value of another field,

Question

<分区>

Answer 1

我会使用 forEach 和 $addToSet，这样脚本就可以重新执行。

The $addToSet operator adds a value to an array unless the value is already present, in which case $addToSet does nothing to that array.

db.collectionname.find().forEach(function(results)
{    
    print( "Id: " + results._id );
    db.collectionname.update( {_id : results._id},
                       {$addToSet : {myArray : results._id}})
});