在mongo shell中的简单解决方案:`

an easy solution in mongo shell: `

use your_db
db.your_collection.createIndex({'1': 1, '2': 1, '3': 1, etc until you reach maximum expected letter count}, {unique: true, dropDups: true, sparse:true, name: 'dropdups'})
db.your_collection.dropIndex('dropdups')

注释:

• 如果您有许多文档，则希望此过程花费很长时间 时间
• 注意，这将删除现有文档，***先克隆您的收藏集，然后在此处尝试.

• if you have many documents expect this procedure to take very long time
• be careful this will remove documents in place, better clone your collection first and try it there.