Google AppEngine

import_transform A single-argument function that returns the correct value and type data based on the external_name or import_template strings. Examples include the built-in Python conversion operators (such as float), any of several helper functions provided in transform, such as get_date_time or generate_foreign_key, a function provided in your own library, or an in-line lambda function. Or, a two-argument function with the keyword argument bulkload_state, which on return contains useful information about the entity: bulkload_state.current_entity, which is the current entity being processed; bulkload_state.current_dictionary, the current export dictionary, and bulkload_state.filename, the --filename argument that was passed to appcfg.py.

import_template Specifies multiple dictionary items for a single property, using Python string interpolation.

How do I handle multipart form data? or How do I handle file uploads to my app? You can obtain the uploaded file data from a multipart form post using classes from the Apache Commons FileUpload package. Specifically you may want to use FileItemStream, FileItermIterator and ServletFileUpload as illustrated below. If you see a java.lang.NoClassDefFoundError after starting your application, make sure that the Apache Commons FileUpload JAR file has been copied to your war/WEB-INF/lib directory and added to your build path. import org.apache.commons.fileupload.FileItemStream;import org.apache.commons.fileupload.FileItemIterator;import org.apache.commons.fileupload.servlet.ServletFileUpload;import java.io.InputStream;import java.io.IOException;import java.util.logging.Logger;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class FileUpload extends HttpServlet {  private static final Logger log =      Logger.getLogger(FileUpload.class.getName());  public void doPost(HttpServletRequest req, HttpServletResponse res)      throws ServletException, IOException {    try {      ServletFileUpload upload = new ServletFileUpload();      res.setContentType("text/plain");      FileItemIterator iterator = upload.getItemIterator(req);      while (iterator.hasNext()) {        FileItemStream item = iterator.next();        InputStream stream = item.openStream();        if (item.isFormField()) {          log.warning("Got a form field: " + item.getFieldName());        } else {          log.warning("Got an uploaded file: " + item.getFieldName() +                      ", name = " + item.getName());          // You now have the filename (item.getName() and the          // contents (which you can read from stream).  Here we just          // print them back out to the servlet output stream, but you          // will probably want to do something more interesting (for          // example, wrap them in a Blob and commit them to the          // datastore).          int len;          byte[] buffer = new

I’m trying to use the bulkuploader for a java program but am running into an interesting issue. My PrimaryKey property is a Long, and in java I can explicitly give them id numbers and they show in the data store as “id=xxx”. When I download the data via the appcfg.py I get a reasonably looking data file. If I reupload the same file it actually inserts things into the data store with key “name=xxx” and therefore doubles every one of my entries.

create a custom uploader using the file upload example provided on appengine’s java FAQ.

App Engine’s datastore is schemaless. That is – it is possible to have Entities of the same Kind with completely different sets of properties. Most of the time, this is a good thing. MySQL, for instance, requires a table lock to do a schema update. By being schema free, migrations can happen lazily, and application developers can check at runtime for whether a Property exists on a given Entity, then create or set the value as needed. But there are times when this isn’t sufficient. One use case is if we want to change a default value on Entities and grandfather older Entities to the new default value, but we also want the default value to possibly be null.