I am in process of designing a reporting tool. the Interface will be C# with backend database. The tool will allow to enter and edit data through an interface and save it to the Database. Additionally, it will provide specific reports, based on the data retrieved from DB.
Currently, I have been trying to solve a M:N relationship in for my DB tables.
The tool lets a user to enter daily Item amounts (Steel and Mesh) based on a Project. I have solved the M:N relationship in the following diagram but I am not sure if this is actually possible and whether I need to break down the daily stats table further, due to a composite key containing 4 PKs from other tables. This is the current diagram i got.
I am wondering whether the diagram has solved the M:N relationship correctly and whether there is a better way to utilise the date table.
I am designing data base for inventory management system which is used by nearly 10 to 15 companies. This database contains nearly 25 tables.For designing database i'm planning to use shared schema architecture(ie each schema corresponding to a company and these all schemas are to be placed in a single database).
i want to know whether it is reliable to use shared schema architecture.
can any one please tell me is it correct decision to use above mentioned architecture.
Thanks in advance..
If I read your question, you are suggesting that each company has its own schema. This means two things:
If you decide to implement a basic change in the schema (ie not a change that one company requests), then you will have to implement this change in all the schemae.
You will probably have to implement different logic in your front
end program for each company.
Better you should develop one schema for the entire database; each table would have a field called 'CompanyID' which naturally would define to which company each row belongs. This field would be a foreign key to the Companies table.
I am making a .NET website which makes uses of a database to store information. It's a practice/experimental project not related to work or uni projects.
My question is to with mapping of the ER diagram to a RelationModel and then onto writing the actual create table statements.
following is my ER:
http://img577.imageshack.us/img577/2405/climsyclipboardf.jpg
i'm confused about the part where an entity has ISA relation so it can be two things.
i know how i can for example map Business Account to Account by including all the attributes of Account into Business Account, but not sure if it makes sense when it comes to create statements.
for example, Account is either business or private account has payment of either CC or Direct Debit. How do i do this in create table statements?
For business vs. private accounts, you can make the account type an attribute of the account by implementing it in a column. Now the same thing can be said about CC and Direct Debit. It really depends on how intricate you want to make this system.
I have a many-to-many relationship in my database of objects A to B. When i create a domain service the metadata looks fine. A has a collections of Bs, B has a collection of As. So it is correct. However the *.g.cs file generated doesn't have the same relationship.
Is there a way to make it work? I googled some answer to actually generate objects for the association table but i am curious if i can avoid this.
Thanks
In the current release/version of RIA Services, you'll need the association table. We will most definitely be looking into this of course for a future release.
That said, I think often many-to-many relationships often have some interesting data associated with the relationship and as such, the middle table often has a real use, rather than existing for the sake of existing.
Till MS implements it in RIA, you can use http://m2m4ria.codeplex.com/
We have used in one of our Silverlight/RIA projects for User/Role (many-to-many) relationship and worked fine.
I'm working on a single database with multiple database schemas,
e.g
[Baz].[Table3],
[Foo].[Table1],
[Foo].[Table2]
I'm wondering why the tables are separated this way besides organisation and permissions.
How common is this, and are there any other benefits?
You have the main benefit in terms of logically groupings objects together and allowing permissions to be set at a schema level.
It does provide more complexity in programming, in that you must always know which schema you intend to get something from - or rely on the default schema of the user to be correct. Equally, you can then use this to allow the same object name in different schemas, so that the code only writes against one object, whilst the schema the user is defaulted to decides which one that is.
I wouldn't say it was that common, anecdotally most people still drop everything in the dbo schema.
I'm not aware of any other possible reasons besides organization and permissions. Are these not good enough? :)
For the record - I always use a single schema - but then I'm creating web applications and there is also just a single user.
Update, 10 years later!
There's one more reason, actually. You can have "copies" of your schema for different purposes. For example, imagine you are creating a blog platform. People can sign up and create their own blogs. Each blog needs a table for posts, tags, images, settings etc. One way to do this is to add a column
blog_id to each table and use that to differentiate between blogs. Or... you could create a new schema for each blog and fresh new tables for each of them. This has several benefits:
Programming is easier. You just select the approppriate schema at the beginning and then write all your queries without worrying about forgetting to add where blog_id=#currentBlog somewhere.
You avoid a whole class of potential bugs where a foreign key in one blog points to an object in another blog (accidental data disclosure!)
If you want to wipe a blog, you just drop the schema with all the tables in it. Much faster than seeking and deleting records from dozens of different tables (in the right order, none the less!)
Each blog's performance depends only (well, mostly anyway) on how much data there is in that blog.
Exporting data is easier - just dump all the objects in the schema.
There are also drawbacks, of course.
When you update your platform and need to perform schema changes, you need to update each blog separately. (Added yet later: This could actually be a feature! You can do "rolling udpates" where instead of updating ALL the blogs at the same time, you update them in batches, seeing if there are any bugs or complaints before updating the next batch)
Same about fixing corrupted data if that happens for whatever reason.
Statistics for all the platform together are harder to calculate
All in all, this is a pretty niche use case, but it can be handy!
To me, they can cause more problems because they break ownership chaining.
Example:
Stored procedure tom.uspFoo uses table tom.bar easily but extra rights would be needed on dick.AnotherTable. This means I have to grant select rights on dick.AnotherTable to the callers of tom.uspFoo... which exposes direct table access.
Unless I'm completely missing something...
Edit, Feb 2012
I asked a question about this: SQL Server: How to permission schemas?
The key is "same owner": so if dbo owns both dick and tom schema, then ownership chaining does apply. My previous answer was wrong.
There can be several reasons why this is beneficial:
share data between several (instances
of) an application. This could be the
case if you have group of reference
data that is shared between
applications, and a group of data
that is specific for the instance. Be careful not to have circular references between entities in in different schema's. Meaning don't have a foreign key from an entity in schema 1 to another entity in schema 2 AND have another foreign key from schema 2 to schema 1 in other entities.
data partitioning: allows for data to be stored on different servers
more easily.
as you mentioned, access control on DB level