When I have a related Resource, I would like to list foreign keys, instead of a url to that resource. How is that possible aside from dehydrating it?
I'm not sure that it's possible without dehydrating the field. I usually have utility functions that handle conversion the dehydration of foreign key and many-to-many relationships, something like this:
#api_utils.py
def many_to_many_to_ids(bundle, field_name):
field_ids = getattr(bundle.obj, field_name).values_list('id', flat=True)
field_ids = map(int, field_ids)
return field_ids
def foreign_key_to_id(bundle, field_name):
field = getattr(bundle.obj, field_name)
field_id = getattr(field, 'id', None)
return field_id
And apply them to the fields like so:
#api.py
from functools import partial
class CompanyResource(CommonModelResource):
categories = fields.ManyToManyField(CompanyCategoryResource, 'categories')
class Meta(CommonModelResource.Meta):
queryset = Company.objects.all()
dehydrate_categories = partial(many_to_many_to_ids, field_name='categories')
class HotDealResource(CommonModelResource):
company = fields.ForeignKey(CompanyResource, 'company')
class Meta(CommonModelResource.Meta):
queryset = HotDeal.objects.all()
dehydrate_company = partial(foreign_key_to_id, field_name='company')
Related
let's say I have a reference data table roles filled with all roles that a user might be granted. The rows are quite stable, meaning that it's uncommon that someone adds a new role to the table. Additionally there's a users table and a join-table users_roles. In fact, the roles table is just required to grant a user some predefined roles by adding a record to users_roles.
The roles table is quite simple:
CREATE TABLE IF NOT EXISTS admin.roles (
id CHAR(16) PRIMARY KEY,
description VARCHAR(256) NOT NULL
);
The following example describes a role:
INSERT INTO admin.roles VALUES('CS_AGENT', 'A customer service agent');
Obviously, I need the possible id values somewhere in my code. This is a set of Strings, but I'd like to prevent magic Strings and make this more type safe.
As far as I understand, there are several options:
create a symbol for each role id
create a new type RoleId that extends String and declare vals
In order to define the set of role ids, these are my options:
use an Enumeration
use a sealed trait/sealed object and derive case objects from it
I'm using JOOQ for my persistence layer, and it would be nice if I could use the type safe RoleId in my queries without manually converting it to String and vice versa.
What would be the best solution for this ?
I am not quite sure I get all of your problem, but would not something like this be the solution?
/** Represents a RoleId from the roles table. */
sealed trait RoleId {
def name: String
def description: String
override final def toString: String = name
}
object RoleId {
case object CS_AGENT extends RoleId {
override val name = "CS_AGENT"
override val description = "A customer service agent"
}
// Define all other roles...
/** All roles */
val allRoles: Set[RoleId] = Set(
CS_AGENT,
// All other roles...
)
/** Returns an RoleId given its name, if the name is not found this will return a None. */
def fromString(name: String): Option[RoleId] = name.toUpperCase match {
case "CS_AGENT" => Some(CS_AGENT)
// All other cases..
case _ => None
}
}
This is completely typesafe and if you need to go to/from a String there are the toString and fromString methods.
The only (big) downside of this approach is a lot of boilerplate code which is easy to screw up - creating a new RoleId but not adding it to the Set, typo in the name or in the case, etc.
An alternative to fixing this is to make this file autogenerated by SBT from some kind of config (even reading the SQL table if reachable in the build environment), for that part this answer of mine to another question may help.
I have following models and serializer the target is when serializer runs to have only one query:
Models:
class Assignee(EmbeddedDocument):
id = ObjectIdField(primary_key=True)
assignee_email = EmailField(required=True)
assignee_first_name = StringField(required=True)
assignee_last_name = StringField()
assignee_time = DateTimeField(required=True, default=datetime.datetime.utcnow)
user = ReferenceField('MongoUser', required=True)
user_id = ObjectIdField(required=True)
class MongoUser(Document):
email = EmailField(required=True, unique=True)
password = StringField(required=True)
first_name = StringField(required=True)
last_name = StringField()
assignees= EmbeddedDocumentListField(Assignee)
Serializers:
class MongoUserSerializer(DocumentSerializer):
assignees = AssigneeSerializer(many=True)
class Meta:
model = MongoUser
fields = ('id', 'email', 'first_name', 'last_name', 'assignees')
depth = 2
class AssigneeSerializer(EmbeddedDocumentSerializer):
class Meta:
model = Assignee
fields = ('assignee_first_name', 'assignee_last_name', 'user')
depth = 0
When checking the mongo profiler I have 2 queries for the MongoUser Document. If I remove the assignees field from the MongoUserSerializer then there is only one query.
As a workaround I've tried to use user_id field to store only ObjectId and changed AssigneeSerializer to:
class AssigneeSerializer(EmbeddedDocumentSerializer):
class Meta:
model = Assignee
fields = ('assignee_first_name', 'assignee_last_name', 'user_id')
depth = 0
But again there are 2 queries. I think that the serializer EmbeddedDocumentSerializer fetches all the fields and queries for ReferenceField and
fields = ('assignee_first_name', 'assignee_last_name', 'user_id')
works after the queries are made.
How to use ReferenceField and not run a separate query for each reference when serializing?
I ended up with a workaround and not using ReferenceField. Instead I am using ObjectIdField:
#user = ReferenceField("MongoUser", required=True) # Removed now
user = ObjectIdField(required=True)
And changed value assignment as follows:
- if assignee.user == MongoUser:
+ if assignee.user == MongoUser.id:
It is not the best way - we are not using ReferenceField functionality but it is better than creating 30 queries in the serializer.
Best Regards,
Kristian
It's a very interesting question and I think it is related to Mongoengine's DeReference policy: https://github.com/MongoEngine/mongoengine/blob/master/mongoengine/dereference.py.
Namely, your mongoengine Documents have a method MongoUser.objects.select_related() with max_depth argument that should be large enough that Mongoengine traversed 3 levels of depth: MongoUser->assignees->Assignee->user and cached all the related MongoUser objects for current MongoUser instance. Probably, we should call this method somewhere in our DocumentSerializers in DRF-Mongoengine to prefetch the relations, but currently we don't.
See this post about classical DRF + Django ORM that explains, how to fight N+1 requests problem by doing prefetching in classical DRF. Basically, you need to override the get_queryset() method of your ModelViewSet to use select_related() method:
from rest_framework_mongoengine.viewsets import ModelViewSet
class MongoUserViewSet(ModelViewSet):
def get_queryset(self):
queryset = MongoUser.objects.all()
# Set up eager loading to avoid N+1 selects
queryset.select_related(max_depth=3)
return queryset
Unfortunately, I don't think that current implementation of ReferenceField in DRF-Mongoengine is smart enough to handle these querysets appropriately. May be ComboReferenceField will work?
Still, I've never used this feature yet and didn't have enough time to play with these settings myself, so I'd be grateful to you, if you shared your findings.
I was told to use automapper in the code below. I cannot get clarification for reasons that are too lengthy to go into. What object am I supposed to be mapping to what object? I don't see a "source" object, since the source is the database...
Would really appreciate any help on how to do this with automapper. Note, the actual fields are irrelevant, I need help with the general concept. I do understand how mapping works when mapping from one object to another.
public IQueryable<Object> ReturnDetailedSummaries(long orgId)
{
var summaries = from s in db.ReportSummaries
where s.OrganizationId == orgId
select new SummaryViewModel
{
Id = s.Id,
Name = s.Name,
AuditLocationId = s.AuditLocationId,
AuditLocationName = s.Location.Name,
CreatedOn = s.CreatedOn,
CreatedById = s.CreatedById,
CreatedByName = s.User.Name,
OfficeId = s.OfficeId,
OfficeName = s.Office.Name,
OrganizationId = s.OrganizationId,
OrganizationName = s.Organization.Name,
IsCompleted = s.IsCompleted,
isHidden = s.isHidden,
numberOfItemsInAuditLocations = s.numberOfItemsInAuditLocations,
numberOfLocationsScanned = s.numberOfLocationsScanned,
numberOfItemsScanned = s.numberOfItemsScanned,
numberofDiscrepanciesFound = s.numberofDiscrepanciesFound
};
return summaries;
}
It is a handy and a timesaver, especially if you use a one to one naming between translations layers. Here is how I use it.
For single item
public Domain.Data.User GetUserByUserName(string userName)
{
Mapper.CreateMap<User, Domain.Data.User>();
return (
from s in _dataContext.Users
where s.UserName==userName
select Mapper.Map<User, Domain.Data.User>(s)
).SingleOrDefault();
}
Multiple Items
public List<Domain.Data.User> GetUsersByProvider(int providerID)
{
Mapper.CreateMap<User, Domain.Data.User>();
return (
from s in _dataContext.Users
where s.ProviderID== providerID
select Mapper.Map<User, Domain.Data.User>(s)
).ToList();
}
It looks like you already have a model? SummaryViewModel?
If this isn't the DTO, then presumably you want to do:
Mapper.CreateMap<SummaryViewModel, SummaryViewModelDto>();
SummaryViewModelDto summaryViewModelDto =
Mapper.Map<SummaryViewModel, SummaryViewModelDto>(summaryViewModel);
AutoMapper will copy fields from one object to another, to save you having to do it all manually.
See https://github.com/AutoMapper/AutoMapper/wiki/Getting-started
The source is your entity class ReportSummary, the target is SummaryViewModel:
Mapper.CreateMap<ReportSummary, SummaryViewModel>();
The best way to use AutoMapper in combination with an IQueryable data source is through the Project.To API:
var summaries = db.ReportSummaries.Where(s => s.OrganizationId == orgId)
.Project().To<SummaryViewModel>();
Project.To translates the properties in the target model straight to the selected columns in the generated SQL.
Mapper.Map, on the other hand, only works on in-memory collections, so you can only use it when you first fetch complete ReportSummary objects from the database. (In this case there may not be much of a difference, but in other cases it can be substantial).
I am developing one application in which data is access from edmx entities and from that we have to fill each business entity after retriving data from edmx entity like:-
var tblproducts = tblproductsData
.Select(t => new tblProduct()
{
CategoryID = t.CategoryID,
Description = t.Description,
ID = t.ID,
Image = t.Image,
InsDt = t.InsDt,
Price = t.Price,
Quantity = t.Quantity,
Status = t.Status,
Title = t.Title,
tblCategory = new EFDbFirst.Models.tblCategory()
{
ID = t.tblCategory.ID,
status = t.tblStatus.StatusID,
Title_Category = t.tblCategory.Title_Category
},
tblStatu = new EFDbFirst.Models.tblStatu()
{
StatusDescription = t.tblStatus.StatusDescription
,
StatusID = t.tblStatus.StatusID
}
});
I am fadeup with this because everytime i have to convert one to another while getting data and setting data in db,
Is there any good way to create some common mehod which takes one anonymous type and converts it to another anonymous type.
Thanks in Advance
Your example isn't that clear.
First of all, EF doesn't work with anonymous types inside itself, it works with the EF types you have defined either using edmx file or code first. You can however create anonymous types yourself by defining an Select statement.
E.g:
var products = context.tblProductsData
.Select(r => new { Description = r.Description }); //new without typename is an
//anonymous object
The tblProduct, tblCategory and tblStatu objects, are they EF types? If so, you don't need to write a Select, EF will generate objects for you when you execute it.
E.g:
var products = context.tblProductsData.ToList();
This will automatically generate tblProduct objects for you. When you try to navigate to tblProduct.tblCategory or tblProduct.tblStatu, lazy loading will retrieve them for you. If you want to explicit load them during first query (eager-loading) use the Include function.
E.g:
var products = context.tblProductsData.Include(r => r.tblCategory)
.Include(r => r.tblStatu).ToList();
However if tblProducts, tblCategory and tblStatu is business objects and NOT EF types, there isn't any other way to do this, you have to explicit create them in a Select statement.
I am using a nested relationship to return grouped messages and was wondering how i can order the nested messages so that they are ordered chronologically.
class MessageGroupResource(ModelResource):
messages = fields.ToManyField('lookup.api.MessageResource', 'message_set', full=True);
class Meta:
queryset = MessageGroup.objects.all();
resource_name = 'message'
authorization= UserAuthorization()
ordering = [
'sendTime',
]
class MessageResource(ModelResource):
messageGroup = fields.ForeignKey(MessageGroupResource, 'messageGroup')
class Meta:
queryset = Message.objects.all()
resource_name = 'submessage'
authorization= UserAuthorization()
This is one way to do it; however, I don't know if there's a better/more API standard way of doing this.
class MessageGroupResource(ModelResource):
messages = fields.ToManyField(MessageResource,
attribute=lambda bundle: bundle.obj.MessageResource.all().order_by("sendTime"))