Check if there is an error in update/insert | MongoDB Java driver

问题

I want to check if an insert fails (due to unique=True index in the collection). If there is an error do something. Bellow is an example of my code.

DBCollection user...;
BasicDBObject Doc = new BasicDBObject(... );

String user_exists = user.insert(Doc).getError(); //insert the doc get error if any
if(user_exists!=null){ //any errors?
    user.update(new BasicDBObject(...)); // error exists so do smthng
}

The above as it is does not work. I believe that the String user_exists is always null. How can I make the above work?

I have seen similar SO questions and mention the WriteConcern which can be passed in the insert(). E.g.

coll.insert(dbObj, WriteConcern.SAFE);

sources: SO question or Mongo docs

However I do not know which one field should I pass (SAFE, ACKNOWLEDGED, UNACKNOWLEDGED etc..) in order to get the error. Maybe I'm pointed in the wrong direction.

I do not wish to raise an exception just to check if there is an error returned by the insert operation.

回答1:

If you are using WriteConcern.ACKNOWLEDGED (which I think is also SAFE) you don't need to pollute your code with error checking.

For ACKNOWLEDGED, the driver will automatically issue a getLastError command automatically and raise an exception if anything got wrong, for example duplicate index violation.

Starting from v2.10 of the Java Driver, the default Write Concern is ACKNOWLEDGED

EDIT

I do not wish to raise an exception just to check if there is an error returned by the insert operation.

You shouldn't do this, but in any case:

The insert method indeed returns WriteResult. If it's getError() is null, everything is OK, otherwise it returns something such as E11000 duplicate key error index:.... For this to work, you will have to use WriteConcern.UNACKNOWLEDGED

来源：https://stackoverflow.com/questions/21588871/check-if-there-is-an-error-in-update-insert-mongodb-java-driver

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