[google-appengine] Re: Datastore update without read
Thanks guys, it really helps! I didn't know about protobuf - thought that u have massive key/value map (so it would be possible to just touch one key). Now it all make sense :) On Oct 12, 1:22 pm, Ikai Lan (Google) ika...@google.com wrote: Thanks Murph. That explanation was dead-on and I couldn't have written a better one myself! You can't just update one column. You're still thinking in RDBMS mode. There is no concept of a column, since to update a property, we need to read the entire entity, deserialize it (it's serialized as protobuf; at its lowest layer BigTable is a key-value store), change the property, reserialize the entire entity and write it. -- Ikai Lan Developer Programs Engineer, Google App Engine plus.ikailan.com | twitter.com/ikai On Tue, Oct 11, 2011 at 2:38 PM, Murph paul.j.mu...@googlemail.com wrote: You can't update just a single property/attribute of an entity unless you already know the values for all of the others. If it's frequently updated, careful use of memcache may allow you to avoid the db.get, but otherwise you have to read it first. An alternative, if you just have say 1 property/attribute which changes often would be to split the entity into two separate entity models, one with the relatively static data, and the other with the frequently changing data. The downside there, of course, is that you're going to have 2 db.get operations when you need all of it, instead of 1. Internally, the datastore is entirely composed of (key, value) pairs, with a single (key,value) per entity (not counting indices, metadata, etc), and the SDK encodes/decodes those values into your entity models for you. They are actually encoded as protobufs, but there's nothing in the datastore's API to modify that data without reading it first. -- You received this message because you are subscribed to the Google Groups Google App Engine group. To view this discussion on the web visit https://groups.google.com/d/msg/google-appengine/-/e6JrqffTES4J. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en. -- You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
[google-appengine] Re: Datastore update without read
You don't even have to do a key fetch beforehand, you can simply persist a new entity with the same key and it will overwrite the existing entity in the datastore. -- You received this message because you are subscribed to the Google Groups Google App Engine group. To view this discussion on the web visit https://groups.google.com/d/msg/google-appengine/-/1PmldOgotYYJ. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
[google-appengine] Re: Datastore update without read
Yeah, but I need to UPDATE one attribute of existing entity (not overwrite the whole entity). On Oct 12, 9:55 am, Gerald Tan woefulwab...@gmail.com wrote: You don't even have to do a key fetch beforehand, you can simply persist a new entity with the same key and it will overwrite the existing entity in the datastore. -- You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
[google-appengine] Re: Datastore update without read
You can't update just a single property/attribute of an entity unless you already know the values for all of the others. If it's frequently updated, careful use of memcache may allow you to avoid the db.get, but otherwise you have to read it first. An alternative, if you just have say 1 property/attribute which changes often would be to split the entity into two separate entity models, one with the relatively static data, and the other with the frequently changing data. The downside there, of course, is that you're going to have 2 db.get operations when you need all of it, instead of 1. Internally, the datastore is entirely composed of (key, value) pairs, with a single (key,value) per entity (not counting indices, metadata, etc), and the SDK encodes/decodes those values into your entity models for you. They are actually encoded as protobufs, but there's nothing in the datastore's API to modify that data without reading it first. -- You received this message because you are subscribed to the Google Groups Google App Engine group. To view this discussion on the web visit https://groups.google.com/d/msg/google-appengine/-/e6JrqffTES4J. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
Re: [google-appengine] Re: Datastore update without read
Thanks Murph. That explanation was dead-on and I couldn't have written a better one myself! You can't just update one column. You're still thinking in RDBMS mode. There is no concept of a column, since to update a property, we need to read the entire entity, deserialize it (it's serialized as protobuf; at its lowest layer BigTable is a key-value store), change the property, reserialize the entire entity and write it. -- Ikai Lan Developer Programs Engineer, Google App Engine plus.ikailan.com | twitter.com/ikai On Tue, Oct 11, 2011 at 2:38 PM, Murph paul.j.mu...@googlemail.com wrote: You can't update just a single property/attribute of an entity unless you already know the values for all of the others. If it's frequently updated, careful use of memcache may allow you to avoid the db.get, but otherwise you have to read it first. An alternative, if you just have say 1 property/attribute which changes often would be to split the entity into two separate entity models, one with the relatively static data, and the other with the frequently changing data. The downside there, of course, is that you're going to have 2 db.get operations when you need all of it, instead of 1. Internally, the datastore is entirely composed of (key, value) pairs, with a single (key,value) per entity (not counting indices, metadata, etc), and the SDK encodes/decodes those values into your entity models for you. They are actually encoded as protobufs, but there's nothing in the datastore's API to modify that data without reading it first. -- You received this message because you are subscribed to the Google Groups Google App Engine group. To view this discussion on the web visit https://groups.google.com/d/msg/google-appengine/-/e6JrqffTES4J. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en. -- You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
