python - Can SQLAlchemy's session.merge() update its result with newer data from the database? -

-

The SQLEEE documentation says, "The present state of an example and its related children were made in collaboration with existing data in the database is."

Does the existing object update with the new data from the database? how? when?

SQLLM has created a single object with each identity in the session. But sometimes you have to recreate something with a known identity, eg. When you get it from the network or when you apply offline lock to avoid long transactions. And when you make an object with known identities that may exist in the database, then there is a chance that the session already tracks an object with this identity. This is what is meant for the merge () method: it engages an object with the session, thus avoiding duplicate objects with the same identification in the session. Below is an example of what is going on: sqlalchemy.orm import * metadata = metadata () T = table ('t', metadata, column ('id', integer, primary_key = true), column ('state ', String (10)), square model: pass mapper (model, t) engine = create_engine (' sqlite: // ') metadata.create_all (engine)) session = sessionmaker (bind = engine) () obj1 = Model () obj1.state = 'value1' session.add (obj1) session.commit () obj_id = obj1.id obj2 = model obj2.id = obj_id obj2 .state = 'value2' obj3 = session.merge ( Obj2) session.commit () print is obj3 obj1, obj3 obj2 print obj3.state

output is:

True False value2

Thus session.merge (obj2) shows that an object with the same identity (Made up of obj1 ), so it merged into the existing code in the obj2 and gives it back.

Below is another example, ate from database: 

  # ... left ... t = table ('t', metadata, column (' Column ('state2', string (10)), column ('state2', string (10)) ... left ... left ... obj1 = 'id', integer, primary_key = true) Model () obj1.state1 = 'value1-1' obj1.state2 = 'value2-1' Session.add (obj1) session.commit () obj_id = obj1.id session.expunge_all () obj2 = model obj2.id = Obj_id obj2.state1 = 'value1-2' obj3 = session.merge (obj2) session .comit () print obj3 obj1, obj3 obj2 print obj3.state1, obj3.state2

Output is: 

  false false value of 1-2 value2-1

Now the object with the same identity was not found in the session, because we dismissed it. Also I partially created a new object with fixed state, but the rest is loaded from the database.


Comments

Post a Comment

Popular posts from this blog

c# - How to capture HTTP packet with SharpPcap -

-
I would like to capture all incoming HTTP packets on my machine. To do this, I am using SharpPcap which is a WinPcap The cover is. SharpPcap works very well, but it captures TCP packets and what it wants to do for me is a very low level. Does anyone know how can I easily get full HTTP requests / reactions from all these TCP packets? Thanks SharpPcap is already able to capture the packet in the same way That's what the virus does (just in the code instead of the GUI). And you can either either parse them directly or you can put them in the drive in the common .pcap file format. The steps to parse the capture are: Open a connection at any time Loop a while Or start capturing using an event callback Parsing the raw packet for the type you want If you are reading .PPP dump files In addition to calling you an offline capture reader is almost the same, there is no need to select an interface, and you can set the majority There is no need to do the modes. All st...
Read more

php - Multiple Select with Explode: only returns the word "Array" -

-
By using Wordpress I have created a multiple selection box so that users can select categories to exclude. When the page is initially loaded, I see my predefined default option. However, when I select a new value and I save ... I only see the word "Array" and have not chosen anything else? & lt; Class = "amultiple" id = "& lt; php echo $ value ['id'] ;? gt;" name = "& gt; php echo $ value ['id'] ;; gt; []" Multiple = "multiple" size = "8" & gt; & Lt ;? Php global option; Foreign currency ($ value as value $) {if (get_settings ($ value ['id']) === FALSE {$$ value ['id'] = $ value ['std']; } And {$$ value ['id'] = get_settings ($ value ['id']); }} $ Ranges = & amp; Amp; Categories ('type = post & orderbiz = name & amp; hide_empty = 1'); If ($ ranges) {$ ex_cat = implode (',', $ tt_cat_exclude); Forex Currency ($ range a...
Read more

php - jQuery AJAX Post not working -

-
I do not understand why this script does not work. It has something to do within AJAX PostScript / Function. Right now, when I submit my form, it runs php code on the same page. What it should do, send the values ​​of the form for Project_Azax.fp, then there will be a refund of success on the page which is correct or false. $ (document) .ready (function () {$ ('div # didIt'). Hide (); $ ('form [name = adminForm]'). Submit (function () ($ {'.post' ('/ project_ajax.php', {action: $ ('[name = action]') Val (), pId: $ ('[name = pId]'). Val (), name ('[Name = name]'. Val (), url: $ ('[url = url]'). Val (), summary: ('[summary = summary]'). Val ()}, Function (data) {if (data.success) {$ ('div # didIt') .Sliddown ('slow');} and {warning ('unsuccessful SA!');}}, 'Jason'); return false ;});}); What is the code for project_ajax.php below ... if ($ _ POST ['action'] == ...
Read more