I have two database. MasterData and ProductData.
I store the Users and Employees in the MasterData and I store the Tasks in the ProdcutData.
A Task entity has a User property. It shows which user created this Task.
If I used just one Database and one DataContext I could define a one and more relationship between two entities. But I must use two Databases and datacontexts.
Are any solution that I define relationship between two entities that are in different databases, datacontexts?
thanks advance: l.
This is not a full blown answer, but it might get you to think of another solution.
Depending on the DBMS you are using, you might be able to create synonyms or updateable views (or something similar) from one database to the other. That you DataContext can contain the synonyms/views and the tables.
In sql-server:
http://msdn.microsoft.com/en-us/library/ms177544.aspx
Well, unless I missed something there is no way to join two entities from different contexts/databases regardless if its L2S or EF. Alternative is pooling all possibly relevant data from two contexts and doing in-memory linq to do relational operations, but that certainly poses performance problems of loading too much data.
Here's a "novel" idea, why not use DataSet? Different table adapters can use different connection strings. It is rather archaic next to L2S/EF but it will offer you most bells & whistles of relationships.
I do have one question, if you keep users and their tasks in separate dbs how do you handle ref integrity?
Synonym is a good solution, but the EF does not support it yet....
http://data.uservoice.com/forums/72025-ado-net-entity-framework-ef-feature-suggestions/suggestions/1052345-support-for-multiple-databases?ref=title
Thanks again!
Related
For a multi-tenancy architecture for a web application using a document-oriented database I can see two conceivable options:
Having one database per tenant, and the collections logically separate different kinds of object.
Having one collection per tenant, and all user data is stored in one database, with some kind of flag or object type identifier on each record.
Have there been any studies or has any documentation been produced regarding these two options and the differences between them?
Is there a particular standard or good reason why someone designing a web application which allows multiple users to store vastly different kinds of data would choose one over the other?
Aside from speed/efficiency issues, are there any other things to be said about this that would influence the decision?
EDIT I'm aware some of the terminology might be database specific, so for all wondering I am specifically referring to MongoDB.
I wouldn't want tenant specific collections. In my application, I usually hard code collection names, in the same way as I'd hardcode table names if I were using SQL tables. There'd be one comments collection that stores all comments for a blog. I would not want to deal with collection names like comments_tenant_1 and comments_tenant_2, because 1) that feels error prone, and 2) would make the application code more complicated (collection names would have to be replaced with functions that computed the collection name). And 3) the number of collections in a single database could grow huge, which would make a list of all collections look daunting, and also MongoDB isn't built for having very many collections (see the link in the comment below your question, which David B posted, https://docs.mongohq.com/use-cases/multi-tenant.html).
However, database names aren't coupled to application data structures, and you can grant permissions on databases (but not on single collections). So one database per tenant could be reasonable. As could be a per document tenant_id field in a single database for all tenants (see the above-mentioned link).
I'm not so good at both Linq and SQL. But I have worked more with SQL and less with LINQ. I've gone through many articles which favors LINQ. I don't want to go the SQL way (i.e. writing stored procedures and operating data etc.)
I want to start with LINQ for every operation related with data. Here are the reasons why I want to do this:
I want to have complete control of my database via application and not by writing stored procs (as I'm not so good at writing store procedure)
I want to create my project as an easy maintainability view
Want faster development
For that, I know that:
I need to add a dbml file, drag and drop tables into that
Use dbContext class, and so on
But I want to know, is there a way:
I can avoid creating dbml file and still be able to access the database?
Do I need to use Linq to Entities for the same?
Will it be a good way to avoid using dbml file? Since for every database changes I need to drop and drop tables every time
Also I've come across many posts where linqToSql is considered deprecated and not a .net future?
I have so many doubts, but I think that's obvious when starting with a new technology?
I found this useful article which is good for beginners:
[http://weblogs.asp.net/scottgu/archive/2010/08/03/using-ef-code-first-with-an-existing-database.aspx][1]
after doing some more research I came to conclusion that:
1)i can avoid creating dbml file and still be able to access database??
ANS Yes but instead of dbml now edmx files will be created.
2)Do I need to use Linq to Entities for the same?
ANS Yes you can go with linq to entities.
3)Will it be good way avoid using dbml file? since for every database changes I need to drop and drop tables every time
ANS it is not required to drop and create again the tables. their are options where you can update selected part of your database and you are not avoiding dbmls. it will created edmx file and that will almost similar to dbmls in many ways.
4) Also I've come across many posts where linqToSql is considered deprecated and not a .net future?
ANS yes in future development it will be depreciated. it supports only sql server as backend.
I hope I'm right. Please do tell me in case any other suggestions.
LINQ is a way to query and project collection of data. For example, you can use LINQ to query and shape data from a database or from an array. LINQ by it self has nothing to with the under lying database.
You use an ORM (Object Relational Mapper) technology to project data stored in tables of a database as collections of objects. Once you have the collection of objects, you can use LINQ to query them.
Now, you have many ORM technologies to select from, such as Entity Framework, NHibernate, Linq2Sql. If you don’t like to maintain a dbml file, have a look at code first approach offered by Entity Framework.
Then there are things called LINQ data providers. They would take a LINQ query, transform it to a SQL targeting a particular database, execute the query and get the results back as a set of objects. Many of the ORMs above has built in LINQ data providers as a part of them and would work behind the scene in fetching the data.
I would advise you to look up on some patterns such Repository and Unit of work for your data layer. When used correctly, these patterns will isolate your data access code from your applications upper layers. This will help you to change your data access technology is it becomes obsolete, without affecting the rest of the application.
LINQ is an awesome technology and you should definitely try it
I have composed the above answer based on my own experience and I am sure there are many SO users with better understanding of the above technologies than myself who may wish to add their own opinion
Good luck
I'm building a project combined of number of sites with common subject.
The sites rely on one central database that holds the common info for all of them.
In addition, each site has another database that holds its unique info (I will refer to it as unique-db in the next lines so I won't be misunderstood).
For example, the Languages table sits in the central db. That said, I suddenly noticed that I need to use the Languages table in one of my unique-db in order for the table to act as a FK so I don't have to create the same table again in the unique-db.
Do I have to create the same table again this time in the unique-db? Or is there a way to connect tables from separate databases?
In addition, we decided using linq2entity and soon we're gonna run some complex queries against the different databases. Will I have a problem with this matter?
How should I go on with that? Was it wise to split the data into a few databases?
I really appreciate all the help I can get!
One thing that might make your life easier is to create views of the central tables in each unique db. Linq to Entities will pick up views as if they were tables.
What are the current options for querying and joining two different Entity Data Models?
I've seen that it's possible to share a single model schema between multiple mapping and storage schemas, but it seems clunky and not encouraged.
The other option I can think of is to query the entities separately and then join the linq objects, but I'm not sure how I feel about dumping all of that into memory.
Does anyone have any better solutions?
The two options you list are the only ones I'm aware of. The former is harder than using a single model, but I wouldn't say "not encouraged." It falls into the unfortunately broad category of "supported Entity Framework features with no support in the GUI designer." The latter option is actually not so bad if you can retrieve only what you need, but will result in retrieving entities from two separate ObjectContexts, which could be awkward if you update. That said, updating objects in multiple contexts, potentially from different databases, is strictly no matter how you do it.
The Entity Framework team had mentioned working on better solutions for the future, but this is a weak point today, and I don't think it's going to change much in v4.
I am developing a website that will manage data for multiple entities. No data is shared between entities, but they may be owned by the same customer. A customer may want to manage all their entities from a single "dashboard". So should I have one database for everything, or keep the data seperated into individual databases?
Is there a best-practice? What are the positives/negatives for having a:
database for the entire site (entity
has a "customerID", data has
"entityID")
database for each
customer (data has "entityID")
database for each entity (relation of
database to customer is outside of
database)
Multiple databases seems like it would have better performance (fewer rows and joins) but may eventually become a maintenance nightmare.
Personally, I prefer separate databases, specifically a database for each entity. I like this approach for the following reasons:
Smaller = faster regarding the queries.
Queries are simpler.
No risk of ever accidentally displaying one customer's data to another.
One database could pose a performance bottleneck as it gets large (# of entities increase). You get a sort of build in horizontal scalability with 1 per entity.
Easy data clean up as customers or entities are removed.
Sure it'll take more time to upgrade the schema, but in my experience modifications are fairly uncommon once you deploy and additions are trivial.
I think this is hard to answer without more information.
I lean on the side of one database. Properly coded business objects should prevent you from forgetting clientId in your queries.
The type of database you are using and how it scales might help you make your decision.
For schema changes down the road, it seems one database would be easier from a maintenance perspective - you have one place to make them.
What about backup and restore? Could you experience a customer wanting to restore a backup for one of their entities?
This is a fairly normal scenario in multi-tenant SAAS applications. Both approaches have their pros and cons. Search on best practices for multi-tenant SAAS (software as a service) and you will find tons of stuff to ponder upon.
Check out this article on Microsoft's site. I think it does a nice job of laying out the different costs and benefits associated with Multi-Tenant designs. Also look at the Multi tenancy article on wikipedeia. There are many trade offs and your best match greatly depends on what type of product you are developing.
One good argument for keeping them in separate databases is that its easier to scale (you can simply have multiple installations of the server, with the client databases distributed across the servers).
Another argument is that once you are logged in, you don't need to add an extra where check (for client ID) in each of your queries.
So, a master DB backed by multiple DBs for each client may be a better approach,
If the client would ever need to restore only a single entity from a backup and leave the others in their current state, then the maintenance will be much easier if each entity is in a separate database. if they can be backed up and restored together, then it may be easier to maintain the entities as a single database.
I think you have to go with the most realistic scenario and not necessarily what a customer "may" want to do in the future. If you are going to market that feature (i.e. seeing all your entities in one dashboard), then you have to either find a solution (maybe have the dashboard pull from multiple databases) or use a single database for the whole app.
IMHO, having the data for multiple clients in the same database just seems like a bad idea to me. You'll have to remember to always filter your queries by clientID.
It also depends on your RDBMS e.g.
With SQL server databases are cheep
With Oracle it is easy to partition tables by customer "customerID", so a single large database can run as fast as a small database for each customer.
However witch every you choose, try to hide it as a low level in your data access code
Do you plan to have your code deployed to multiple environments?
If so, then try to keep it within one database and have all table references prefixed with a namespace from a configuration file.
The single database option would make the maintenance much easier.