I have a .Net Core 2.1 Web API which talks to two MySQL databases. Therefore I have two DbContexts, each with a connection string pointing to the relevant database.
In one of my controller actions, I need to return data which requires a join between two tables, one from each database. Is it possible to do this?
As an example, a simple controller action to retrieve data might look something like this:
[HttpGet]
public IEnumerable<Employee> GetEmployees()
{
return _context.Employees
.Include(e => e.Departments);
}
That example uses one controller only, because in that example both the employee and department tables are in the same database, and therefore both their DbSets would be in the same DbContext.
But what if the employee table was in one database and department table was in another? Then the DbSets for employee and department would be defined in different DbContexts. How could I handle the join in that case? (So that in the example above, the "Include" works properly?
I would imagine that I would have to inject both DbContexts into this controller. But I'm not sure where to go from there...
In my case, both datbases are MySQL databases, and both are on the same server, so that is the only scenario I'm interested in.
After more research, it looks like I could maybe use raw SQL to achieve this. However, what I ended up doing is creating a view on the server which does all the necessary joins, and then I simply call this view...
Related
I'm using Codeigniter and Doctrine together for a project. I've gotten everything set up with both of these tools. But I'm not sure where I should have this bit of code:
$query = $em->createQuery('SELECT u FROM sessions u');
$sessions = $query->getResult(); // array of User objects
Should I be putting this in the controller or in the models/entities? At first thought, I figured I should put this kind of logic in the Sessions model, but it requires the entities manager $em, which I had thought should have been in the controller.
Thanks, this has been driving me crazy for the past half hour.
A lot of people like to create objects called DAOs or Data Access Objects to store this type of information.
The DAO contains the entity manager and methods that can be called and return the data you need. For example this function would reside in a DAO:
function findEmployeeById($emp_id)
And it would contain the query used to retrieve an employee from the database. In your controller you would just use the DAO instead of having an entity manager and dealing with it at that level.
But it really depends on preference and how large your project is.
I am currently working on a project where we are rewriting software that was originally written in Visual DataFlex and we are changing it to use SQL and rewriting it into a C# client program and a C#/ASP.Net website. The current database for this is really horrible and has just had columns added to table or pipe(|) characters stuck between the cell values when they needed to add new fields. So we have things like a person table with over 200 columns because stuff like 6 lots of (addressline1, addressline2, town, city, country, postcode) columns for storing different addresses (home/postal/accountPostal/ect...).
What we would like to do is restructure the database, but we also need to keep using the current structure so that the original software can still work as well. What I would like to know is would it be possible using Linq to write a DataContext Object Model Class that could sort of interpret the data base structures so that we could continue to use the current database structure, but to the code it could look like we where using the new structure, and then once different modules of the software are rewritten we could change the object model to use the correct data structure???
First of all, since you mention the DataContext I think you're looking at Linq to SQL? I would advice to use the Entity Framework. The Entity Framework has more advanced modeling capabilities that you can use in a scenario as yours. It has the ability to construct for example a type from multiple tables, use inheritance or complex types.
The Entity Framework creates a model for you that consists of three parts.
SSDL which stores how your database looks.
CSDL which stores your model (your objects and the relationships between them)
MSL which tells the Entity Framework how to map from your objects to the database structure.
Using this you can have a legacy database and map this to a Domain Model that's more suited to your needs.
The Entity Framework has the ability to create a starting model from your database (where all tables, columns and associations are mapped) en then you can begin restructuring this model.
These classes are generated as partial so you could extend them by for exampling splitting the database piped fields into separate properties.
Have you also thought about using Views? If possible you could at views to your database that give you a nicer dataschema to work with and then base your model on the views in combination with stored procedures.
Hope this gives you any ideas.
I'm building a multi-tenant app with a shared database using .NET MVC 3 and PetaPoco.
The tenant id (along with other info) is saved in a FormsAuth cookie on login and is available to all controllers via a BaseController property. Most tables, (i.e. apart from apart the main 'Tenants' table) include a TenantId column.
Instead of manually adding a 'WHERE TenantId = X' to all CRUD on the feature tables, is there a way I can dynamically add this to the query just before its executed? In other words, maybe maintain a list of tables, and if the query is for one of those tables, then dynamically add in the TenantId filter?
The benefit of course is that it removes the need to add in the filter manually thus reducing the chances its left out. I did find an example using NHibernate, which I doubt can be repurposed. I am using Ninject in case that makes a difference.
There is an OnCommandExecuting method on the Database class which you can override in your own sub class, and modify the sql as you wish just before it gets executed. We use this feature for converting isnull/nvl between Sql Server and Oracle.
You could just leave a marker in your sql and replace it here.
I have these two tables in my database:
client.Employee
employee.Employee
When I try to import this into entity framework I get two table objects created:
Employee
Employee1
Is there a way to handle naming conflicts that will work better than this? And really, I would prefer that my schema is represented some how for non conflicting tables as well.
Unfortunately no. Information about schema is only included in storage description (SSDL) and it is not passed to conceptual model (CSDL) so in conceptual model you have two entities named Employee and EF is using the most basic way to resolve that. Another problem is that this probably cannot be modified because generating model from database is not driven by any T4 template which can be changed whereas reverse processing (generating SQL database creation script from model) is.
I am designing a project in asp.net mvc3, i have designed my database in sql server, add i am using ado.net.
This is my controller action
public ViewResult ProductFormulationIndex()
{
return View(db.ProductFormulation.ToList());
}
means i want to display all fields of ProductFormulation table.
this is my table:-
and this is my productCategory Table
in my ProductFormulationIndex.cshtml i want to display Code of ProductCategory Table, not only id. So what should i do in controller or in Model for it ?
you may suggest tutorial related to it.
Thanks in advance.
You need a view model which is specifically designed for the view.
When defining your view models you shouldn't be thinking in terms of tables. SQL tables have absolutely no meaning in a view. Think in terms of what information you need to show and define your view models accordingly.
Therefore, You can define a view model like:
public class ProductInformation
{
...
public string CategoryCode {get; set;}
...
}
Or public Category ProductCategory.
You can use AutoMapper to convert between your real models and the view model you have defined.
You can find a good tutorial at http://weblogs.asp.net/shijuvarghese/archive/2010/02/01/view-model-pattern-and-automapper-in-asp-net-mvc-applications.aspx
Although I may not answer your question you are touching on some interesting points.
I subscribe to the school of thought that says one should not query an object model but rather make use of a denormalized lightweght query layer.
You will pobably quickly run into the lazy-loading and projection issue: i.e. you do not always require the related data and you do not always require all the fields. A query layer takes care of this quite nicely since using a denormalized model means that when you do your query you do not need to do N-number of joins to get the related data. You will still at some point need to gather up the data but you actual view queries will be order fo magnitude faster.
Also, getting all the data (by joining) for your denormalized model is a once-off affair as opposed to doing it each and every time you display the relevant data on the front-end.
Hope that makes sense :)