Categories: Java

Google Datastore Query Get By ID & Filter – Code Example

Following are code samples on Google App Engine Datastore Query and how to get entities by id and based on filters.

Get Entity By Id

Pay attention to the code “datastore.get(KeyFactory.createKey( “savedreport”, reportId). “savedreport” is the name of entity.

DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();  
 Entity entity = null;
 try {
  entity = datastore.get(KeyFactory.createKey("savedreport", reportId));
 } catch(EntityNotFoundException e) {
  e.printStackTrace();
 }

Get Entity By One Filter

Pay attention to “setFilter” method

Filter createdByFilter = new FilterPredicate("created_by", FilterOperator.EQUAL, userId );
Query query = new Query("sqm").setFilter( createdByFilter );    

DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
List entities = datastore.prepare(query).asList( FetchOptions.Builder.withLimit( count ) );

Get Entity By Multiple Filter

Pay attention to usage of multiple FilterPredicate methods and CompositeFilterOperator and setFilter method called on Query.

Filter dateMinFilter = new FilterPredicate("sprint_enddate", FilterOperator.GREATER_THAN_OR_EQUAL, beginDate );
Filter dateMaxFilter = new FilterPredicate("sprint_enddate", FilterOperator.LESS_THAN_OR_EQUAL, endDate );  
Filter nameFilter = new FilterPredicate("project_id", FilterOperator.EQUAL, projectId );  
Filter createdByFilter = new FilterPredicate("created_by", FilterOperator.EQUAL, createdBy );
Filter rangeFilter = CompositeFilterOperator.and( nameFilter, createdByFilter, dateMinFilter, dateMaxFilter );
Query query = new Query("sqm").setFilter( rangeFilter );    

DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
List entities = datastore.prepare(query).asList( FetchOptions.Builder.withLimit( count ) );

Ajitesh Kumar

I have been recently working in the area of Data analytics including Data Science and Machine Learning / Deep Learning. I am also passionate about different technologies including programming languages such as Java/JEE, Javascript, Python, R, Julia, etc, and technologies such as Blockchain, mobile computing, cloud-native technologies, application security, cloud computing platforms, big data, etc. For latest updates and blogs, follow us on Twitter. I would love to connect with you on Linkedin. Check out my latest book titled as First Principles Thinking: Building winning products using first principles thinking. Check out my other blog, Revive-n-Thrive.com