I have Entity Framework Models similar to :
Category
Content
NewsCategory (Inherits Category)
News ( Inherits Content)
I use TPH inheritance for both newscategory and news . I have a TYPE field in my DB. if type=1 means News ( in content table) and again if type=1 means ( in NewsCategory table).
category and cntent have many to many relationship!
but when I want to add news how can I prevent to add news with other type ?
when I add a news it want categoryId and I can use 1,2 or other Id!
#
if fact I want to create many to many relation ship between news and news category AND category and content . and I want news dont know any thing about content and its relation ship
Database doesn't understand meaning of TPH inheritance - it has many-to-many association between Categories and Contents table and it indeed allows creating relation between any category and content. You cannot avoid it in TPH on database level but on entity level you should have navigation properties only in your derived types so handling it on application level should be straight forward.
I tend to define enums to accompany the inheritance classes I define.
public enum CategoryType
{
News = 1,
Photography,
PopularMusic
}
public enum ContentType
{
Article = 1,
Image,
Video
}
You two tables could have a TypeId and so when your code writes a news item.
Category.TypeId = (int)CategoryType.News;
and
Content.TypeId = (int)ContentType.Article;
You can't avoid having to do this is code, but it should be clearer and less error prone that just throwing an INT value at a typeId filed.
In your case I'm not sure of your relationships, such as where the Type field is (I assumed there'e one in Category and also one in Content). You seem to have missed something when you wrote type=1 means ( in NewCategory table) in you question.
I'm not sure why you would need to add a categoryId when adding a news as news inherits from Content and not Category did you mean TypeId?
Related
I am new with MDS, and I have a question about one to many relation mapping in MDS
I have a product, contains descriptions in multiple languages. I have created two entities with derived hierarchy structure: product (P_ID, P_name)and Addtional description(P_ID, P_Name_in_German, P_name_in_English).
Additonal description is a drop down from product table from MDS UI, but I only want to populate info that releated with its same P_ID. How can I achieve that? Can I use business rules here and how it should look like?
(2012 Master data service' web interface)
I have also faced a similar problem. I have decided to add multiple fields for languages and apply business rules for them. Let's see how it would work for your entity:
Product entity
{
Code
Name
Name_in_English (text)
Name_in_German (text)
Default_language (domain based, points to Languages entity)
}
Languages entity
{
Code
Name
}
Add values to the Languages entity:
Code = "EN", Mane = "EN"
Code = "DE", name = "DE"
Now we need to add the following business rules to the Product entity:
BR1:
{
IF Condition - Equals: Default_language equals "EN"
THEN Action - Change value: Name = Name_in_English
}
BR2:
{
IF Condition - Equals: Default_language equals "DE"
THEN Action - Change value: Name = Name_in_German
}
After that You will see the product names in your product entity only in proper language which is chosen by drop-down field Default_language.
The second option:
If You want user to see only the Name field and don't want him to see additional fields,
You can hide those fields (Name_in_English and Name_in_German) by setting their width to zero.
Moreover, You can use attribute groups to separate two modes of view:
first mode (for the regular user) - You see only Code and Name
second mode (for the administrator) - You see fields: Name_in_English, Name_in_German, Default_language.
For it to work You need to create two attribute groups:
1) attribute group "EN" (add attributes Name and Code to the group)
2) attribute group "DE" (add attributes Name_in_English, Name_in_German, Default_language to the group)
Hope something of that is helpful!
You're missing something. You said you have a derived hierarchy structure but you don't show a domain based attribute on the Additional description entity with a pointer back to the Product entity. Perhaps you were thinking that the P_ID for Additional Description is the pointer back but it isn't (based on your explanation). It is the entity Code identifier for the Additional Description entity and not the key you need that points back to Product. Perhaps you meant One to One. One to Many implies you have a separate Parent_P_ID back to the Product entity.
Add the Domain Based Parent_P_ID attribute to the Additional Description entity and then reconstruct your derived hierarchy structure. This may not be that helpful because I think you have left something out of the explanation of what you are trying to do.
Hi Cocunuts,
We can not assign derived hierarchy to entities in MDS 2012,but we can achieve this in MDS 2016 , Your Domain based attribute(Drop down) cannot be further filtered in MDS 2012.
We need to allow users to customize their entities like products... so my intention was to have a product table and a custom_product table with just the information the users are allowed to change.
When a client goes to the product I want to merge the information, means I want to merge the two tables - the custom overwrites the default Products table.
I know that in mysql there exists a ifnull(a.title, b.title) way but I was wondering if there is any nice and efficient way to solve this in Rails 4 with Active Record. Assume that the products and custom products table have just 2 columns, ID and TITLE
I think you can convert both objects to JSON and then handle their params as a hash, using the merge method:
class Product
end
class Customization
belongs_to :product
end
a = Product.find(...)
b = a.customization
c = JSON(a.to_json).merge(JSON(b.to_json).reject!{|k,v| v.nil?})
Therefore c will contain all params from Product eventually overridden by those in Customization which are not nil.
If you still want to use a Product object with hybrid values (taken from Customization) you can try this:
a.attributes = a.attributes.merge(b.attributes.reject!{|k,v| v.nil?})
In this case a will still be a Product instance. I would recommend to keep the same attributes in both models when doing this.
I am using struts2 , hibernate and MySql for my project.
I have table name TimeTable having 42 columns (all long datatype) containing course codes.
I want to search "column names" having particular course code from a particular row.
Help me please.
If you have mapped the entity in a "proper" way in hibernate, the answer is obvious:
You will have an entity called TimeTable, which have 42 relationships to Course (I bet the attribute name will be course1, course2.... course42).
The resulting HQL is simply a bunch of OR
from TimeTable t
where t.course1.code = :something
OR t.course2.code = :something .....
However, it is obviously a bad model design. You should make Timetable and Course a Many-To-Many relationship, and have another table storing the relationship. So, in the entity, you will see something like
class TimeTable {
#ManyToMany
private List<Course> courses;
}
Your life will be much easier with such design.
Suppose I have 3 tables in sqlalchemy. Users, Roles and UserRoles defined in declarative way. How would one suggest on doing something like this:
user = Users.query.get(1) # get user with id = 1
user_roles = user.roles.query.limit(10).all()
Currently, if I want to get the user roles I have to query any of the 3 tables and perform the joins in order to get the expected results. Calling directly user.roles brings a list of items that I cannot filter or limit so it's not very helpful. Joining things is not very helpful either since I'm trying to make a rest interface with requests such as:
localhost/users/1/roles so just by that query I need to be able to do Users.query.get(1).roles.limit(10) etc etc which really should 'smart up' my rest interface without too much bloated code and if conditionals and without having to know which table to join on what. Users model already has the roles as a relationship property so why can't I simply query on a relationship property like I do with normal models?
Simply use Dynamic Relationship Loaders. Code below verbatim from the documentation linked to above:
class User(Base):
__tablename__ = 'user'
posts = relationship(Post, lazy="dynamic")
jack = session.query(User).get(id)
# filter Jack's blog posts
posts = jack.posts.filter(Post.headline=='this is a post')
# apply array slices
posts = jack.posts[5:20]
I am currently evaluating SQLAlchemy for a project. Here is my schema:
a LANGUAGE table, with a row for each language supported
a TRANSLATION table with (ID, LANGUAGE_ID, STR)
various tables will, instead of storing text, store TRANSLATION_IDs, for example, BOOK(ID, TITLE_TRANSLATION_ID, ABSTRACT_TRANSLATION_ID)
Now, assuming each request has the current language ID available (for example, through a thread variable...), I would need SQLAlchemy to automatically join the TRANSLATION table, and thus have text fields in the current language. Something like:
class Book(Base):
id = Column(Integer, primary_key=True)
title = TranslatableText()
abstract = TranslatableText()
When retrieving, the ORM would automatically join to the TRANSLATION table with the current language ID, and my_book.title would give me the title in the current language.
I also need this to work across relations: if a class contains foreign keys to other classes that also contain translatable text fields, I would ideally like those to be retrieved too.
Lastly, I would also need to be able to get to the TRANSLATION_ID for each field, for example through my_book.title_translation_id.
I am not expecting a complete solution, but I'd like to know if something like this is feasible, and where to start.
You have to use the concept of http://docs.sqlalchemy.org/en/latest/orm/extensions/declarative.html#mixin-and-custom-base-classes
Create one top level class and write some funciton like read, write and create. Always call that function to create or read data from the database.
If you dont want to implement the mixin classes then also you can use event http://docs.sqlalchemy.org/en/latest/orm/events.html#sqlalchemy.orm.events.MapperEvents.translate_row