Assume:
class Contacts(db.Model):
first_name = StringProperty()
last_name = StringProperty()
phone_number = PhoneNumberProperty()
new_contact = Contacts(first_name="Homer", last_name="Simpson", phone_number = 1234566)
new_contact.put()
I am new to GAE Datastore, but per GAE Datastore Docs (see below if interested), i can't modify a single property of the entity (eg, phone_number). I have to re-declare all properties, and then put() the new entity. Omitting previously-declared properties from the new entity results in them being declared as None. Is there a workaround for this -- such as manually overriding the key-name generation function -- so the entity maintains the same key?
#
from GAE Datastore Docs:
To update an existing entity, modify the attributes of the object, then call the put() method. The object data overwrites the existing entity. The entire object is sent to the datastore with every call to put(). Note: The datastore API does not distinguish between creating a new entity and updating an existing entity. If the object's key represents an entity that exists, calling its put() method overwrites the entity.
that's not true. You need to have a way to get the contact you want and you can update just that. Using the keyname is only one way to do it. If you know the ID of filter a query to only get one entity, you can update a field from it and the put() to update it.
You could have something like:
query = Contact.all().filter('first_name', 'john').filter('last_name', 'doe')
for contact in query:
contact.phone_number = 498340594834
contact.put()
Note that that code would update any contacts with that name to that phone number. If there is more than one with that name, both are updated. Using a keyname can prevent that but you have to create more complex keys since only the first and last name might colide.
Related
To enter data into the Cosmos DB Tables, I use this addition (https://github.com/tomlm/iciclecreek.bot/tree/master/source/Libraries/Iciclecreek.Bot.Builder.Dialogs.Database.AzureStorage). The problem is that I cannot pass the value of the variable to the entity. Only the name of the variable is passed, not its content. My variable only contains a string value and is outputted for validation without any problem.
In this add-on, I use the Entity Operation block.
//Content Entity
// ${dialog.cosmos.name} - my variable whose value needs to be passed
{
"partitionKey": "KeyP2",
"rowKey": "RowKeyR1",
"nameUs": "${dialog.cosmos.name}",
"surnameus": "feleni"
}
You need to set a property with all variables before the entity operation block. And then insert this property into the Entity.
https://i.stack.imgur.com/xqo75.png
I've been working through Adrian Hall's book on integrating Xamarin and Azure Mobile Apps. In Chapter 3 he adds a User table to facilitate "Friends" data. In his implementation, the client authenticates the user and then makes a request to a custom endpoint that either adds the user to the database or updates their record. Here's an abridged version of the method in the custom controller:
[HttpGet]
public async Task<IHttpActionResult> Get()
{
// ...Obtain user info
User user = new User()
{
Id = sid,
Name = name,
EmailAddress = email
};
dbContext.Users.AddOrUpdate(user);
dbContext.SaveChanges();
// ...
}
The trouble is, the 2nd time the same user logs in to the app, this code throws an exception saying
Modifying a column with the 'Identity' pattern is not supported. Column: 'CreatedAt'. Table: 'CodeFirstDatabaseSchema.User'.
This StackOverflow Answer explains that this is because the AddOrUpdate() method nulls out any properties not set on the entity, including CreatedAt, which is an identity column. This leaves me with a couple of questions:
What is the right way to Add or Update an entity if the CreatedAt value cannot be edited? The same SO thread suggests a helper method to look up the existing CreatedAt and apply it to the entity before trying to save it. This seems cumbersome.
Why is this implemented as a custom auth controller that returns a new Auth token when it only needs to add or update a User in a database? Why not use a normal entity controller to add/update the new user and allow the client to continue using the Auth token it already has?
For the CustomAuthController.cs code, see here.
When you focus on what you are trying to do from SQL perspective it would be like:
update dbo.some_table set some_primary_key = new_primary_key where some_primary_key = ...
which would result in cannot update identity column some_primary_key which makes sense.
But if you do have a reason to update the PK you still can do it if you set the identity insert
SET IDENTITY_INSERT dbo.some_table ON;
Then after you made an insert you set it off using similar syntax.
But this is rather exceptional scenario.
Usually there is no need to manually insert PKs.
Now going back to EF.
The error you are getting is telling you that you cannot modify a column with PK, most likely user_id and/or some other columns if you have composite PK.
So, first time round a new user gets created. Second time round, because you are suing GetOrUpdate a user gets udpated but because you are passing PK it breaks.
Solution?
AddOrUpdate was meant to help with seeding the migrations only.
Given its destructive nature I would not recommend using GetOrUpdate anywhere near production.
You can replace GetOrUpdate with two operations Get and Update
Fetch user and then
if not exists then create a new one
or if it does exist then update it
Please I want to give custom IDs to my database objects in Firebase but I don't now how to do it. Firebase creates default IDs for database objects which I don't want. I want to be able to assign my own IDs to objects or the child nodes of in the database for unique identification.
Most likely you're adding the items to the database with something like:
ref.push().set("my value");
This generates a new unique key under ref and sets your value on it.
If you want to use you own key/name for the child location, add the item with:
ref.child("my key").set("my value");
You cannot customize ID of firebase object, but you can create another field with ID role.
ref.child("my_id").set("customize_id");
after that, using "Filter by key" to get exactly your object you want.
In our case: We need to have a user_id type Int and auto-increase, so we can't use default _id of firebase object, we create user_id ourself to solve this problem.
I have 2 entities, User and Profile. Profile has in-symfony relation with User, but there is no in-database relation (no foreign key, no cascade) - only simple int column named user_id and nothing more.
Problem is obvious: when i delete user - associated profiles persists, but their user_id points to non-existing user row.
Since I use in-symfony relations when i fetch profile from database it fetches also related user entity. I expected that if there is no row with specific ID, it would just leave null or at least throw an exception or something.
Problem is that symfony creates empty User entity object with only id set. rest of its fields are null.
I know solution would be to create FK, constraints etc ... but I'm not allowed to touch anything in database schema.
How can I manage this problem ? I could even leave those empty object if only i had simple way to determine if they exist in database inside TWIG - so i would know if i can display {{ profile.user.email }} for example.
Fast and dirty solution, as you ask, is to use this test: http://twig.sensiolabs.org/doc/tests/defined.html
But I strongly recommend to rework your entity relations.
Found solution: its fetch: EAGER set to problematic mapping in doctrine.
By default doctrine uses LAZY fetching what results in using Proxy classes generated by doctrine for related entity. That class is almost same as real entity class. Difference is inside getter methods that before returning value performs fetching entity from database.
At this point, when you call getter on such proxy, doctrine tries to find entity in database using its ID, and since it doesn't find anything it throws exception.
When using EAGER fetching doctrine performs fetching of related entities on the same time when it fetches main entity and if it doesn't find it then sets null on relation field.
I've got an ASP.NET MVC app that uses Linq to Sql for data access.
Say I have two objects: An Order object that has a foreign key to a Customer object by CustomerID. So, in my Order class, you would see two properties: an int CustomerID field, and an EntityRef member accessible by a Customer property.
When the edits or submits an Order, my MVC app will update the CustomerID field directly of the Order class, instead of updating the Customer property. This saves us from having to fetch a customer record, and I can use the default model binding code to fill the property automatically as long as the submitted form request has a customerID entry.
This works ok, however, later on in some other part of the code--say a business rules portion, some logic will access the Customer property of the Order object. For example:
if (order.Customer.HasPreviousOrders) then ...
Even though the CustomerID field is set, the Customer field is null, so this business rule throws an exception.
I know Linq 2 Sql uses EntityRefs to do delayed loading. My question is: is there a way to trigger the delayed loading on an object's EntityRef if the ID field has been modified?
We have a dynamic rules engine, so I don't have control of what foreign key objects are going to be needed. I'd rather not have to go through all my controllers to set the EntityRef<> values directly.
Thanks for the help.
Ok, no takers. It looks like what I'm trying to do is just not doable--or maybe not a good idea.
I went ahead and implemented code so I am setting the association object property instead of the ID property so the business rules can be processed.