java - How to be avoid duplicates entries at insert to MongoDB -

i want shure when inputting new dbobject db unique , collection doesn't contain key field duplicates .

here how looks now:

public abstract class abstractmongodao<id, model> implements genericdao<id, model> {      protected mongo client;      protected class<model> model;      protected dbcollection dbcollection;      /**      * contains model data : unique key name , name of method      */     protected keyfield keyfield;      @suppresswarnings("unchecked")     protected abstractmongodao() {         parameterizedtype genericsuperclass = (parameterizedtype) this.getclass().getgenericsuperclass();         model = (class<model>) genericsuperclass.getactualtypearguments()[1];         getkeyfield();     }      public void connect() throws unknownhostexception {         client = new mongoclient(config.getmongohost(), integer.parseint(config.getmongoport()));         db clientdb = client.getdb(config.getmongodb());         clientdb.authenticate(config.getmongodbuser(), config.getmongodbpass().tochararray());         dbcollection = clientdb.getcollection(getcollectionname(model));     }      public void disconnect() {         if (client != null) {             client.close();         }     }      @override     public void create(model model) {         object keyvalue = get(model);         try {             objectmapper mapper = new objectmapper();             string requestasstring = mapper.writerwithdefaultprettyprinter().writevalueasstring(model);             // check if not presented             basicdbobject dbobject = new basicdbobject((string) keyvalue, requestasstring);             dbcollection.ensureindex(dbobject, new basicdbobject("unique", true));             dbcollection.insert(new basicdbobject((string) keyvalue, requestasstring));         } catch (throwable e) {             throw new runtimeexception(string.format("duplicate parameters '%s' : '%s'", keyfield.id(), keyvalue));         }     }  private object get(model model) {     object result = null;     try {         method m = this.model.getmethod(this.keyfield.get());         result = m.invoke(model);     } catch (exception e) {         throw new runtimeexception(string.format("couldn't find method name '%s' @ class '%s'", this.keyfield.get(), this.model.getname()));     }     return result; }  /**  * extract name of collection specified @ '@entity' annotation.  *  * @param clazz model class object.  * @return name of collection specified.  */ private string getcollectionname(class<model> clazz) {     entity entity = clazz.getannotation(entity.class);     string tablename = entity.value();     if (tablename.equals(mapper.ignored_fieldname)) {         // think usual logger         tablename = clazz.getname();     }     return tablename; }  private void getkeyfield() {     (field field : this.model.getdeclaredfields()) {         if (field.isannotationpresent(keyfield.class)) {             keyfield = field.getannotation(keyfield.class);             break;         }     }     if (keyfield == null) {         throw new runtimeexception(string.format("couldn't find key field @ class : '%s'", model.getname()));     } } 

keyfeld custom annotation:

@retention(retentionpolicy.runtime) @target(elementtype.field) public @interface keyfield {      string id();      string get();      string statusprop() default "all"; 

but i'm not shure solution prove this. i'm newly @ mongo.

any suggestions?

a uniqueness can maintained in monbodb using _id field. if not provide value of field, mongodb automatically creates unique id particuler collection.

so, in case create property called _id in java & assign unique field value here. if duplicated, throw exception.