I have a main table for gather Real Estate records. This table has relations with other reference data tables, so in summary it contains IDs for:
CountryId
TypeId
PurposeId
CurrencyId
etc...
There are other tables like Countries, Types, Purposes, etc ...
When creating a new Real Estate record, based on the "Type", there are some "Extended Properties" defined. So user has to enter values for those "Extended Properties" that are directly linked to the selected "Type".
An example of Extended Property something as:
Bedrooms
This property might have 1 or more values like:
1
2
3
I am storing a table of Extended Properties and another for Extended Property Values, as one Property might have one or more values.
For a given Type, there might be one or more such properties, hence I had to define a new table to link:
RealEstate ID
ExtendedProperty ID
ExtendedProperty Value ID
Now, the website offers a search engine, user can enter search criteria for the following fields:
Country
Type
Purpose
One or more Extended Property (based on the Type selected and its related Properties)
I need to query the DB and return full data records, i.e. When I return a Real Estate record, I need to return the TypeID + TypeName and CountryID + CountryName, etc ... In other words, I need to join all those tables and then query with the values I received from the search criteria, and such a criteria can be something as:
CountryId = 1
Type = 2
EP (1,5) (Find me a Real Estate record that has an Extended Property whose ID is "1" and has a value for that property equal to Extended Property Value ID of "5".
etc ...
I believe, all other tables, its a matter of normal join and checking on some parameters, but its gets harder when I have to query the Extended Properties.
Much appreciated.
Related
I am currently trying to model a MongoDB database structure where the entities are very complex in relation to each other.
In my current collections, MongoDB queries are difficult or impossible to put into a single aggregation. Incidentally, I'm not a database specialist and have been working with MongoDB for only about half a year.
To keep it as simple as possible but necessary, this is my challenge:
I have newspaper articles that contain simple keywords, works (oevres, books, movies), persons and linked combinations of works and persons. In addition, the same people appear under different names in different articles.
Later, on the person view I want to show the following:
the links of the person with name and work and the respective articles
the articles in which the person appears without a work (by name)
the other keywords that are still in the article
In my structure I want to avoid that entities such as people occur multiple times. So these are my current collections:
Article
id
title
keywordRelations
KeywordRelation
id
type (single or combination)
simpleKeywordId (optional)
personNameConnectionIds (optional)
workIds (optional)
SimpleKeyword
id
value
PersonNameConnection
id
personId
nameInArticleId
Person
id
firstname
lastname
NameInArticle
id
name
type (e.g. abbreviation, synonyme)
Work
id
title
To meet the requirements, I would always have to create queries that range over 3 to 4 tables. Is that possible and useful with MongoDB?
Or is there an easier way and structure to achieve that?
Suppose I have following 4 collections:
1- posts
2- companies
3- groups
4- users
Bellow is my current structure in post:
and their relation is:
A company has an owner and many other members (user collection).
A group has many members (users).
A user has many posts.
A group has many posts that published by one of its members.
A company has many posts that published by its owner or members.
Now i have a problem on storing relation of users, company, and group with posts collection.
Bellow is my current structure:
I have decided to have a field postable inside my post document, and has a type field that will be 'user', or 'group', or 'company', and two other fields name, and id that will be company/group id and company/group name in cases that post is belonged to company or group but not user means type="group" || type="company".
Now how i can handle this to map id as FK of group and company collection (one field FK of two collection) ?
Is it the right structure ?
What you have here is a polymorphic association. In relational databases, it is commonly implemented with two fields, postable_id and postable_type. The type column defines which table to query and id column determines the record.
You can do the same in mongodb (in fact, that is what you came up with, minus the naming convention). But mongodb has a special field type precisely for this type of situations: DBRef. Basically, it's an upgraded id field. It carries not only the id, but also collection name (and database name).
how i can handle this to map id as FK of group and company collection (one field FK of two collection)?
Considering that mongodb doesn't have joins and you have to load all references manually, I don't see how this is any different from a regular FK field. Just the collection name is stored in the type field now, instead of being hardcoded.
I have a MS SQL 2008 database, and I can't change its schema. I have to work with what it is.
It has three tables that relevant to the question.
Product table. The columns are:
Id (identity, PK)
Group (NOT NULL)
SubGroup (NOT NULL)
Code (Unique, NOT NULL)
Description
Contract table. The columns are:
Id (identity, PK)
Code (NOT NULL)
Descritpion
Discount table. The columns are:
Id (identity, PK)
Type (restricted to one of the four values:
'product',
'group',
'subgroup' or
'contract') (NOT NULL)
Object (depending on the value of Type refers one of the four:
Product.Code
Product.Group
Product.SubGroup
Contract.Code) (NOT NULL)
Value (NOT NULL)
The idea is that the discount can be applied to either of the four. I'd like to reiterated, that this is the database design that I can't change.
With Entity Framework I can query the tables all right with joins but I can't use navigation properties out of the box, because navigation properties are generated based on foreign key relationships from database, and you can't define "conditional" relationship in MS SQL, where the field object relates to one table when field type contains this value and relates to another table when the value is different.
My question is this: Is this possible to define classes and mappings with Entity Framework, so that I can use navigation properties in this scenario? For example, I do Discount.Object and I receive either Contract object or Product object in response, and if this is a Product object it's retrieved on the right property.
Is this, or something similar possible, or joins is the best I can do?
You said that "this is the database design that I can't change", but without changing existing tables, can you at least add views?
If you can, you can create a view for the Discount table that has four different nullable columns for each relationship. That would map nicely in EF as four navigation properties.
After you do that, if you still want a combined column, you could add your own property to the Discount entity that will return an object by checking which of the four navigation properties is not null, and returning the linked entity.
You cannot create a relational database like this. You need separate columns for the keys to each potential parent row.
Is there a way within the entity framework designer to duplicate an entity and then apply a filter condition to both to make them unique. Id like to retain all navigation properties and what not.
For example, say in the database I had a table of orders. I could have two entities, one called IncompleteOrders and One called Complete based on the same table, with the complete having a filter specified on the database field 'complete'.
Thanks in advance
Yes, this is called Table per Hierachy
You have one physical table, which has a special, single, scalar column which is used as a discriminator.
Like this:
OrderId OrderName IsComplete
1 Foo 1
2 Bar 1
3 FooBar 0
Where IsComplete is the discriminator (BIT column, for example), so when you setup your entities on your EDMX, you create three entities:
1. Orders
2. CompleteOrders (derives from Orders)
3. InCompleteOrders (derives from Orders)
On the table mapping for Orders, you say "Maps to CompleteOrders, when IsComplete = 1", and "Maps to InCompleteOrders, when OrderType = 0".
Good writeup on TPH/Discriminator pattern here.
Tables
Departments
Employees
I'm trying to associate:
Departments - dept_code : char(4)
Employees - dept : varchar(4)
But I receive the following error,
Error 2039: The conceptual side
property 'DEPT_CODE' has already been
mapped to a storage property with type
'char'. If the conceptual side
property is mapped to multiple
properties in the storage model, make
sure that all the properties in the
storage model have the same type.
Other than changing the field's data type on the database side... Is there are workaround to this?
Just change the type. I would also change the name to either dept or dept_code for all tables so that it is consistent.