Mongo database how to use email as unique key?

问题

I creted a mongodb collection and wanted to mark "email" field as unique in it, so I did this (it's a Java code though language isn't actually important here):

IndexOptions indexOptions = new IndexOptions();
indexOptions.unique(true);
userCollection.createIndex(Indexes.text("email"), indexOptions);

Then I try to insert 2 documents like so:

Document doc = new Document();
doc.append("email", "johnny@gmail.com");
doc.append("username", "John");
doc.append("lastname", "Doe");
userCollection.insertOne(document);

Document doc = new Document();
doc.append("email", "duck@gmail.com");
doc.append("username", "Donald");
doc.append("lastname", "Duck");
userCollection.insertOne(document);

The first one inserts without any problems, the second one throws this exception:

E11000 duplicate key error collection: wagon.w_users index: email_text dup key: { : "com", : 0.6666666666666666 }

If I change gmail.com to e.g. gmail.comm, it throws this exception

E11000 duplicate key error collection: wagon.w_users index: email_text dup key: { : "gmail", : 0.6666666666666666 }

The workaround I see is to hash user's email and create a field like "emailhash" but it looks like a crutch to me. Maybe I'm missing some important setting here? Can we use email as unique key at all?

回答1:

The error come from your index creation : you're creating a text index by using

userCollection.createIndex(Indexes.text("email"), indexOptions);

So mongodb parse your string around '@' and '.', and indexes extracted words. As your index is annotated with 'unique' option, your second insert fails. Instead of that, create a simple ascending index :

userCollection.createIndex(Indexes.ascending("email"), indexOptions);

来源：https://stackoverflow.com/questions/52442590/mongo-database-how-to-use-email-as-unique-key