google datastore filter

import com.google.appengine.api.datastore.DatastoreServiceFactory;import com.google.appengine.api.datastore.DatastoreService;import com.google.appengine.api.datastore.Query.Filter;import com.google.appengine.api.datastore.Query.FilterPredicate;import com.google.appengine.api.datastore.Query.FilterOperator;import com.google.appengine.api.datastore.Query.CompositeFilter;import com.google.appengine.api.datastore.Query.CompositeFilterOperator;import com.google.appengine.api.datastore.Query;import com.google.appengine.api.datastore.PreparedQuery;import com.google.appengine.api.datastore.Entity;

// Get the Datastore ServiceDatastoreService datastore = DatastoreServiceFactory.getDatastoreService();

Filter heightMinFilter =  new FilterPredicate("height",                      FilterOperator.GREATER_THAN_OR_EQUAL,                      minHeight);//一个查询对应一个过滤器Filter用FilterPredicate;heightMaxFilter =  new FilterPredicate("height",                      FilterOperator.LESS_THAN_OR_EQUAL,                      maxHeight);

//Use CompositeFilter to combine multiple filtersFilter heightRangeFilter =  CompositeFilterOperator.and(heightMinFilter, heightMaxFilter);//一个查询对应多个Filter用CompositeFilter,搭建过滤器

Filter

// Use class Query to assemble a queryQuery q = new Query("Person").setFilter(heightRangeFilter);

// Use PreparedQuery interface to retrieve resultsPreparedQuery pq = datastore.prepare(q);

for (Entity result : pq.asIterable()) {  String firstName = (String) result.getProperty("firstName");  String lastName = (String) result.getProperty("lastName");  Long height = (Long) result.getProperty("height");

  System.out.println(firstName + " " + lastName + ", " + height + " inches tall");}

google datastore filter