Database handling using Entity Framework - c#

I have two questions for database handling using Entity Framework. I am using SQL Server 2012/14 web api 2 (VS 2012/13) but it doesn't matter because my question is regarding code first approach for EF6. In code first approach if the table does not exist that EF creates it for you (EF's awesome feature).
1.) Usually when EF creates a table, it uses nvarchar for string datatype but I need to use varchar. How can I specify that in EF? (Also for other datatypes?)
2.) Also I need to create stored procedure using EF (if it does not exist in DB). And also how can I invoke it from EF? Stored Procedure takes input parameter and gives output records.
In case of any change in model or logic, it should be reflected automatically in DB. [Very Important]
Request: Please keep the understanding level of your explanation to be Super Easy. I have just saw some YouTube videos and trying to understand it and implement it on my project. But I don't want to just copy code, I want to understand it so please kindly provide explanation for each line. Multiple solution will be appreciated. (I mean Data Annotation and Fluent API both)
My Last Option: I was thinking of creating script and executing it in "up" function (where migration happens and creates all SQL object) But issue with that approach is that if there is any change in my model, I have to reflect the same changes in that script too as it is hard coded. I am going to use this option when I have no other choice left. I haven't tried this option yet so I might be completely wrong about it.
Thanks in advance.

1) If you want to specify the database type to be used in the actual column of your table, here is the code (using Fluent API) for it:
modelbuilder.Entity<Department>()
.Property(p => p.Name)
.HasColumnType("varchar");
Source: https://msdn.microsoft.com/en-us/data/jj591617#1.10
2) If you want Entity Framework to generate the script that would create your desired stored procedure, have a look at this article: https://msdn.microsoft.com/en-us/data/dn468673. I don't think it would be a good idea to copy the source code from there and paste it over here, so if you have any specific questions, feel free to ask.
If you want to create the stored procedure script yourself and then invoke it using Entity Framework, then have a look at this article: https://msdn.microsoft.com/en-us/data/jj557860. Note: this option tends to have a maintenance cost associated to it. But it is worth doing it if the stored procedure generated by Entity Framework is not as efficient as your version of how the stored procedure should be written as.
Again please feel free to ask any specific questions here.

Related

.Net MVC Database first model with stored procedures

I'm developing a MVC5 web project in VS 2013 and I have to use an already existing database and its Stored Procedures so I'm looking forward to using Entity Framework database first approach to help me model the classes.
My question is, should I create the classes (the model) directly from the tables using EF? i mean should my classes represent a table in the database exactly the way they are? - given that some stored procedures return a combination of different attributes from different tables, I'm confused as what the classes on the code should represent exactly.
Also i want to have my own form to let users upload and read their info, so scaffolding the views to create the read/update/delete won't come handy for this task, will it?
Thanks!
If it is code first then you can use the EF tools to scaffold your database for you from your existing database. If it's database first, all of the database models are generate for you anyway and whenever you update your database the models can be updated to reflect the changes for you.
If you are using stored procedures for code first, you'll need to create objects for each stored procedure so that the return values can be mapped back to an object. These should really match precisely the data that is being returned back in both type and naming:
this.Database.SqlQuery<YourEntityType>("storedProcedureName",params);
As for having your views scaffolded for you, I think you should take one step at a time and see what works for your use case or not.

Entity framework change in database

What to do when changing database on Entity Framework
Hi,
I am using Microsoft Entity Framework with C#. I used a code first method so that entity framework created some magic code for me so that i didnt need to write it. Now, i need to change my database a bit. Need to add columns in the table and so on. How can i do this? Is there any other option that applying code first method again?? I found this solution a little bit cruel so i ask for help. Haven't found anything useful on google so i try here.
Thx
When updating the database using the code first approach, you want to use Migrations.
http://msdn.microsoft.com/en-us/data/JJ591621.aspx
It automatically scans your changes and creates a Migration object for each set of changes.
There is some steps that you need to take, and I think it is better to refer you to the original documentation of it on MSDN:
You can find your solution here:
http://msdn.microsoft.com/en-us/library/jj591621.aspx
look at the parts that talks about Enabling Migrations and Generating & Running Migrations.

Is it a good approach to query the database only through stored procedures?

When I am developing an ASP.NET website I do really like to use Entity Framework with both database-first or code-first models (+ asp.net mvc controllers scaffolding).
For an application requiring to access an existing database, I naturally thought to create a database model and to use asp.net mvc scaffolding to get all the basic CRUD operations done in a few minutes with nearly no development costs.
But I discussed with a friend who told me that accessing data stored in the database only through stored procedures is the best approach to take.
My question is thus, what do you think of this sentence? Is it better to create stored procedures for any required operations on a table in the database (e.g. create and read on this table, update and delete only on another one, ...)? And what are the advantages/disadvantages of doing so instead of using a database-first model created from the tables in the database?
What I thought at first is that it double costs of development to do everything through stored procedures as you have to write these stored procedures where Entity Framework could have provided DbContext in a few clicks, allowing me to use LINQ over Entities, ... But then I've read a few stuff about Ownership Chains that might improve security by setting only permissions to execute stored procedures and no permissions for any operations (select, insert, update, delete) on the tables.
Thank you for your answers.
Its a cost benefit analysis. Being a DB focused guy, I would agree with that statement. It is best. It also makes you code easier to read (no crazy sql statements uglifying it). Increased performance with cached execution plans. Ease of modifying the querying without recompiling the code, eetc.
Many of the ppl I work with are not all that familiar with writing SPROCs so it tends to be a constant fight with them use them. Personally I dont see any reason to ever bury SQLStatments in your code. They tend to shy away from them b/c it is more work for them up front.
Yes, it's a good approach.
Whether it's the best approach or not, that depends on a lot of factors, some of them which you don't even know yet.
One important factor is how much furter development there will be, and how much maintainence. If the initial development is a big part of the total job, then you should rather use a method that gets you there as fast and easy as possible.
If you will be working with and maintaining the system for a long time, you should focus less on the initial development time, and more on how easy it is to make changes to the system once it's up and running. Using stored procedures is one way to make the code less depending on the exact data layout, and allows you to make changes without a lot of down time.
Note that it's not neccesarily a choise between stored procedures and Entity Framework. You can also use stored procedures with Entity Framework.
This is primarily an opinion based question and the answer may depend on the situation. Using stored procedure is definetely one of the best ways to query the database but since the emergence of Entity Framework it is widely used. The advantage of Entity Framework is that it provides a higher level of abstraction.
Entity Framework applications provide the following benefits:
Applications can work in terms of a more application-centric conceptual model, including types with inheritance, complex members,
and relationships.
Applications are freed from hard-coded dependencies on a particular data engine or storage schema.
Mappings between the conceptual model and the storage-specific schema can change without changing the application code.
Developers can work with a consistent application object model that can be mapped to various storage schemas, possibly implemented in
different database management systems.
Multiple conceptual models can be mapped to a single storage schema.
Language-integrated query (LINQ) support provides compile-time syntax validation for queries against a conceptual model.
You may also check this related question Best practice to query data from MS SQL Server in C Sharp?
following are some Stored Procedure advantages
Encapsulate multiple statements as single transactions using stored procedured
Implement business logic using temp tables
Better error handling by having tables for capturing/logging errors
Parameter validations / domain validations can be done at database level
Control query plan by forcing to choose index
Use sp_getapplock to enforce single execution of procedure at any time
in addition entity framework will adds an overhead for each request you make, as entity framework will use reflection for each query. So, by implementing stored procedure you will gain in time as it's compiled and not interpreted each time like a normal entity framework query.
The link bellow give some reasons why you should use entity framework
http://kamelbrahim.blogspot.com/2013/10/why-you-should-use-entity-framework.html
Hope this can enlighten you a bit
So I'm gonna give you a suggestion, and it will be something I've done, but not many would say "I do that".
So, yes, I used stored procedures when using ADO.NET.
I also (at times) use ORM's, like NHibernate and EntityFramework.
When I use ADO.NET, I use stored procedures.
When you get data from the database, you have to turn it into something on the DotNet side.
The quickest thing is to put data into a DataTable or DataSet.
I no longer favor this method. While it may make for RAPID development ("just stuff the data into a datatable")......it does not work well for MAINTENANCE, even if that maintenance is only 2-3 months down the road.
So what do I put the data into?
I create DTO/POCO objects and hydrate the data from the database into these objects.
For example.
The NorthWind database has
Customer(s)
Order(s)
and OrderDetail(s)
So I create a csharp class called Order.cs, Order.cs and OrderDetail.cs.
These ONLY contain properties of the entity. Most of the time, the properties simple reflect the columns in the database for that entity. (Order.cs has properties, that simulate a Select * from dbo.Order where OrderID = 123 for example).
Then I create a child-collection object
public class OrderCollection : List<Order>{}
and then the parent object gets a property.
public class Customer ()
{
/* a bunch of scalar properties */
public OrderCollection Orders {get;set;}
}
So now you have a stored procedure. And it gets data.
When that data comes back, one way to get it is with an IDataReader. (.ExecuteReader).
When this IDataReader comes back, I loop over it, and populate the Customer(.cs), the Orders, and the OrderDetails.
This is basic, poor man's ORM (object relation mapping).
Back to how I code my stored procedures, I would write a procedure that returns 3 resultsets, (one db hit) and return the info about the Customer, the Order(s) (if any) and the OrderDetails(s) (if any exist).
Note that I do NOT do alot of JOINING.
When you do a "Select * from dbo.Customer c join dbo.Orders o on c.CustomerID = o.CustomerId, you'll note you get redundant data in the first columns. This is what I do not like.
I prefer multiple resultsets OVER joining and bringing back a single resultset with redundant data.
Now for the little special trick.
Whenever I select from a table, I always select all columns on that table.
So whenever I write a stored procedure that needs customer data, I do a
Select A,B,C,D,E,F,G from dbo.Customer where (......)
Now, alot of people will argue that. "Why do you bring back more info than you need?"
Well, real ORM's do this anyway. So I am poor-man reflecting this.
And, my code for taking the resultset(s) from the stored procedure to turn that into instances of objects........stays consistent.
Because if you write 3 stored procedures, and each one selects data from Customer table, BUT you select different columns and/or in a different order, youre "object mapper" code needs to have a method for each stored procedure.
This method of ADO.NET has served me well.
And, once my team swapped out ADO.NET for a real ORM, and that transition was very pain free because of the way we did the ADO.NET from the get go.
Quick rules of thumb:
1. If using ADO.NET, use stored procedures.
2. Get multiple result-sets, instead of redundant data via joins.
3. Make your columns consistent from any table you select from.
4. Take the results of your stored procedure call, and write a "hydrater" to take that info and put into your domain-model as soon as you can. (the .cs classes)
That has served me well for many years.
Good luck.
In my opinion :
Stored Procedures are written in big iron database "languages" like PL/SQL or T-SQL
Stored Procedures typically cannot be debugged in the same IDE your write your UI.
Stored Procedures don't provide much feedback when things go wrong.
Stored Procedures can't pass objects.
Stored Procedures hide business logic.
Source :
http://www.codinghorror.com/blog/2004/10/who-needs-stored-procedures-anyways.html

How to call a stored Procedure for SELECT in EF4 to populate an EntityDataSource

I was trying to investigate the use of EF4 for my project and I faced this "interesting" problem.
Creating the edmx, there is an easy way to connect the entities to a user interface component (DevExpress GridView for instance) passing through the EntityDataSource.
Question: Do you think is there a better way to bind my entities to controls?
Now as a client specification I would be happy to interact with the database through stored procedures (for update, insert, select, delete) limiting then the power of EF, but still it would give me some benefits.
Question: Is there a way to use a select stored procedure as it is done for insert/update/delete and continue using EntityDataSource?
Question: Do you think it is a reasonable solution to populate the entities with database views in order to pilot the select and use the stored procedure mapping otherwise?
Thank you for your help and thoughts.
The first question is somewhat open in nautre, and rather dependent on the controls you are using, and the design pattern (if any) that you are trying to adhere to. From a development perspective, if you are Unit Testing you should always consider seperation of concerns, and how tightly you want to bind your controls to your 'domain'. Is this an ASP.NET application?
The second question is quite common, especially in enterprise scenarios where you have security concerns and serious DBAs (!). You CAN implement select stored procedures. I'd suggest reading the post found here.
As for the third question, again it is possible to use views in Entity Framework. There are several articles and pitfalls, I'd certainly check this article first as well.
2 and 3 really come down to the clients requirements. On my current project, we are using stored procedures for create, update and delete operations, whilst allowing direct select access on our tables as necessary. This is effective as it allows you to use the native power of EF and LINQ in terms of dynamic queries. Again, this suits our requirements, but may not suit yours!
EDIT:
I just wanted to provide a couple more links regarding your last comment, as they deal more explicitly with EntityDataSource. The relevant SO article is here, and it links to a nice article here, which should help you.
EDIT:
One more option is to add a defining query to control how EF performs the select. See here.
Nick.

How to use a local database in c#?

I've made a local database for a C# project:
I know basic SQL commands, but haven't worked with databases in C#.
What I'd like to know specifically is:
How to read from the database (query)
How to add and update rows
The database only consists of 3 tables, so I don't think anything fancy is needed.
First, you should learn a bit about various technologies and APIs for connecting with a database.
The more traditional method is ADO.NET, which allows you to define connections and execute SQL queries or stored procedures very easily. I recommend digging up a basic tutorial on ADO.NET using Google, which may differ depending on what type of project you're creating (web app, console, WinForms, etc).
Now days, ORMs are becoming increasingly popular. They allow you to define your object model in code (such as every database table would be a class, and columns would be properties on that class) and bind to an existing database. To add a new row to a table, you'd just create an instance of a class and call a "Save" method when you're done.
The .NET framework has LINQ to SQL and the Entity Framework for this sort of pattern, both of which have plenty of tutorials online. An open source project I really like is Castle Active Record, which is built on top of NHibernate. It makes defining ORMs quite easy.
If you have specific questions about any of the above, don't hesitate to post a new question with more specific inquiries. Good luck!
Update:
I thought I'd also put in one last reference as it seems you might be interested in working with local database stores rather than building a client/server app. SQLite allows you to interact with local stores on the file system through SQL code. There's also a .NET binding maintained by the SQLite guys (which would in theory allow you to work with the other platforms I mentioned): http://system.data.sqlite.org/index.html/doc/trunk/www/index.wiki
You can use SQLCE.
This blog will give you a good start.
http://weblogs.asp.net/scottgu/archive/2011/01/11/vs-2010-sp1-and-sql-ce.aspx
Here is a small tutorial that should be helpful to you.
You can make use of the SqlDataReader to read data
and the SqlCommand to Insert Update Delete rows from your tables.
http://www.dotnetperls.com/sqlclient
You could use it by adding following to your Startup.cs
services.AddDbContext<DemoDbContext>(options => options.UseSqlite("Filename=data.db"));

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