I am currently working towards implementing a charting library with a database that contains a large amount of data. For the table I am using, the raw data is spread out across 148 columns of data, with over 1000 rows. As I have only created models for tables that contain a few columns, I am unsure how to go about implementing a model for this particular table. My usual method of creating a model and using the Entity Framework to connect it to a database doesn't seem practical, as implementing 148 properties for each column does not seem like an efficient method.
My questions are:
What would be a good method to implement this table into an MVC project so that there are read actions that allow one to pull the data from the table?
How would one structure a model so that one could read 148 columns of data from it without having to declare 148 properties?
Is the Entity Framework an efficient way of achieving this goal?
Entity Framework Database First sounds like the perfect solution for your problem.
Data first models mean how they sound; the data exists before the code does. Entity Framework will create the models as partial classes for you based on the table you direct it to.
Additionally, exceptions won't be thrown if the table changes (as long as nothing is accessing a field that doesn't exist), which can be extremely beneficial in a lot of cases. Migrations are not necessary. Instead, all you have to do is right click on the generated model and click "Update Model from Database" and it works like magic. The whole process can be significantly faster than Code First.
Here is another tutorial to help you.
yes with Database First you can create the entites so fast, also remember that is a good practice return onlye the fiedls that you really need, so, your entity has 148 columns, but your app needs only 10 fields, so convert the original entity to a model or viewmodel and use it!
One excelent tool that cal help you is AutoMapper
Regards,
Wow, that's a lot of columns!
Given your circumstances a few thoughts come to mind:
1: If your problem is the leg work of creating that many properties you could look at Entity Framework Power Tools. EF Tools is able to reverse engineer a database and create the necessary models/entity relation mappings for you, saving you a lot of the grunt work.
To save you pulling all of that data out in one go you can then use projections like so:
var result = DbContext.ChartingData.Select(x => new PartialDto {
Property1 = x.Column1,
Property50 = x.Column50,
Property109 = x.Column109
});
A tool like AutoMapper will allow you to do this with ease via simply configurable mapping profiles:
var result = DbContext.ChartingData.Project().To<PartialDto>().ToList();
2: If you have concerns with the performance of manipulating such large entities through Entity Framework then you could also look at using something like Dapper (which will happily work alongside Entity Framework).
This would save you the hassle of modelling the entities for the larger tables but allow you to easily query/update specific columns:
public class ModelledDataColumns
{
public string Property1 { get; set; }
public string Property50 { get; set; }
public string Property109 { get; set; }
}
const string sqlCommand = "SELECT Property1, Property50, Property109 FROM YourTable WHERE Id = #Id";
IEnumerable<ModelledDataColumns> collection = connection.Query<ModelledDataColumns>(sqlCommand", new { Id = 5 }).ToList();
Ultimately if you're keen to go the Entity Framework route then as far as I'm aware there's no way to pull that data from the database without having to create all of the properties one way or another.
Related
I have a specific EF Core 6.x question.
If the SQL table has a column removed. Then EF Core will throw a SqlException saying that it's an invalid column name unless I also update the C# model.
For example,
Create Table User
(
FirstName varchar(200)
,MiddleName varchar(200) null -- tried to remove this column after table is created
,LastName varchar(200)
)
I tried deleting the MiddleName column from the SQL Table. When I run a simple read call using EF Core 6, I get the error.
c# model
public class User
{
public virtual string FirstName { get; set; }
public virtual string? MiddleName { get; set; }
public virtual string LastName { get; set; }
}
var db = new EFDbContext(connectionString);
var data = db.Users.ToList(); // SqlException here after column removal
Is there any way to remove columns from the table without needing to update the c# class as well?
Tried making the C# property MiddleName not virtual.
Update:
In the event that I have an existing application. I would need to modify the c# model even if the codebase doesn't refer to the removed column anywhere. Alternatively, I can decorate the property with [NotMapped] or use the Ignore() method in the modelbuilder.
Both approaches means a rebuild of the assembly is needed and downtime during deployment.
NHibernate's mapping can be done using an XML file and thus all it takes would be a simple config file update.
I can't seem to find anything in EF Core that will reduce the headache of maintaining older codebases when schema changes occur.
EF creates a data model mapping internally to track the database schema and your code models. By removing the column in your database table, your code model no longer matches the database. Hence, the exception occurs.
This is definitely not be the answer you're looking for, but as far as I know EF Core need consistency between the models and the DB schemas to work.
I can think of 2 things here:
Maybe you could benefit from using a different ORM (Did you give Dapper a cahnce)
You might be facing an architectural issue, if there's more than one team working with the same database, and more than one system calling that database, the best way to avoid headaches in the future would be to isolate the data access layer and expose an API that serves all the involved systems.
That way, if the database changes, you just need to re-build the data access layer, no downtime for your clients.
And finally... in my opinion the ideal solution is a combination of both, create a decoupled data access layer, map things there and expose an API with the models your application needs.
I have linked 2 Entities Project, Train with a many to many relationship.
Now, I want to add an existing Train to Project.Trains. Unfortunately, the collection has a lot of entries. When I write project.Trains.Add(...) it materializes the complete collection and this takes a lot of time. Is there a way to tell EF that I want to add the Train to the Project without materializing the collection, so that the action is faster?
Assuming that the Train.Projects collection will have fewer items than its Project.Trains counterpart, a quick solution would be adding the Project to the Train instead of the other way around:
train.Projects.Add(project);
Yes, there is a way of doing it, but it is very difficult, and it involves digging into the very interna of EF. If you use the proxies generated by EF, they will typically implement IEntityWithRelationships. You will be able to access the relationship manager as
var entityWithRelationships = project as IEntityWithRelationships;
var relatedEnd = entityWithRelationships.RelationshipManager.GetRelatedEnd("RelationshipName as found in Metadata");
With this setup you should be able to add the Train as follows:
context.Trains.Add(train);
relatedEnd.Add(train);
As said, it is a long way to make it work, but it would solve your problem.
You can:
1- Turn off lazy loading. This way, accessing Trains doesn't make a
query to DB. But be aware of the side effects because you may have
already relied on it.
2- Close to Relational Database world: Add FK property to Train entity and set it on the newly created
object:
newTrain.ProjectId = project.Id
3- Even more Close to Relational Database world: Add junction table of ProjectTrain, to implement Many-to-Many relation
public class ProjectTrain
{
public int Id {get;set;}
public Project Project {get;set;}
public Train Train {get;set;}
}
and add this to the context:
DBSet<ProjectTrain> ProjectTrains {get;set;}
and finally, make a new entity of ProjectTrains and set the Train and Project properties
I have to take data from an existing database and move it into a new database that has a new design. So the new database has other columns and tables than the old one.
So basically I need to read tables from the old database and put that data into the new structure, some data won't be used anymore and other data will be placed in other columns or tables etc.
My plan was to just read the data from the old database with basic queries like
Select * from mytable
and use Entity Framework to map the new database structure. Then I can basically do similar to this:
while (result.Read())
{
context.Customer.Add(new Customer
{
Description = (string) result["CustomerDescription"],
Address = (string) result["CuAdress"],
//and go on like this for all properties
});
}
context.saveChanges();
I think it is more convenient to do it like this to avoid writing massive INSERT-statements and so on, but is there any problems in doing like this? Is this considered bad for some reason that I don't understand. Poor performance or any other pitfalls? If anyone has any input on this it would be appreciated, so I don't start with this and it turns out to be a big no-no for some reason.
Something that you could perhaps also try, is merely to write a new DBContext class for the new target database.
Then simply write a console application with a static method which copies entities and properties from the one context to the other.
This will ensure that your referential integrity remains intact and saves you a lot of hassle in terms of having to write SQL code, since EF does all the heavy lifting for you in this regard.
If the dbContext contains a lot of entity dbsets I recommend that you use some sort of automapper.
But, this depends on the amount of data that you are trying to move. If we are talking terrabytes, I would rather suggest you do not take this approach.
I have determined a relational model makes more sense for a particular collection in a database. The problem is, the domain model was originally started with an embedded model and there is a large amount of UI code that expects it to be in this form. Updating the database schema isn't an issue, but I'm curious if there is any easy way around remodeling the C# domain objects to a more old-fashioned relational model. I've started writing mappers (with AutoMapper) between version one and version two (see classes below), but it's getting messy really quick.
Below is some fictitious code that outlines a similar domain model.
// Existing
class MyClass
{
List<Event> Events { get; set; }
List<Movie> Movies { get; set; }
}
// How it should have been modeled
class MyClass
{
List<int> Events { get; set; } // Stores Event IDs
List<int> Movies { get; set; } // Stores Movie IDs
}
The database will have to be normalized.
If I have to remodel the domain model, that's fine; I just want to feel comfortable I've exhausted other possibilities that might save time. Is there an easy solution to this problem I'm overlooking?
If the only purpose of your restructuring is the relational database I'd advise you to look into O/R mapping. An O/R mapper, like NHibernate or the Entity Framework, should be able to map your existing embedded model to a relational database. Using an O/R mapper can take away the need of remodeling your domain.
Given the specific problem, it seemed the only two options I could justify were the two I mentioned in my initial post (map the data manually or change my domain object). Ultimately, for me, the path of least resistance was to map the data manually. I appreciate the suggestion by pjvds, but I couldn't justify switching to a new ORM at this stage of the project considering so many other things work better with the C# MongoDB driver and also considering a mapper isn't necessary for the other portions of our database.
Okay, so i've studied c# and asp.net long enough and would like to know how all these custom classes i created relate to the database. for example.
i have a class call Employee
public class Employee
{
public int ID { get; set; }
public string Name { get; set; }
public string EmailAddress { get; set; }
}
and i have a database with the following 4 fields:
ID
Name
EmailAddress
PhoneNumber
it seems like the custom class is my database. and in asp.net i can simple run the LINQ to SQL command on my database and get the whole schema of my class without typing out a custom class with getter and setter.
so let's just say that now i am running a query to retrieve a list of employees. I would like to know how does my application map to my Employee class to my database?
by itself, it doesn't. But add any ORM or similar, and you start to get closer. for example, LINQ-to-SQL (which I mention because it is easy to get working with Visual Studio), you typically get (given to you by the tooling) a custom "data context" class, which you use as:
using(var ctx = new MyDatabase()) {
foreach(var emp in ctx.Employees) {
....
}
}
This is generating TSQL and mapping the data to objects automatically. By default the tooling creates a separate Employee class, but you can tweak this via partial classes. This also supports inserts, data changes and deletion.
There are also tools that allow re-use of your existing domain objects; either approach can be successful - each has advantages and disadvantages.
If you only want to read data, then it is even easier; a micro-ORM such as dapper-dot-net allows you to use our type with TSQL that you write, with it handling the tedious materialisation code.
Your question is a little vague, imo. But what you are referring to is the Model of the MVC (Model-View-Controller) architecture.
What the Model , your Employee Class, manages data of the application. So it can not only get and set (save / update) your data, but it can also be used to notify of a data change. (Usually to the view).
You mentioned you where using SQL, so more then likely you could create and save an entire employee record by sending an Associative Array of the table data to save it to the database. Your setting for the Class would handle the unique SQL syntax to INSERT the data. In larger MVC Frameworks. The Model of your application inherits several other classes to handle the proper saving to different types of backends other than MS SQL.
Models will also, normally, have functions to handle finding records and updating records. This is normally by specify a search field, and it returning the record, of which would include the ID and you would normally base this back into a save / update function to make changes to record. You could also tie into this level of the Model to create revision of the data you are saving
So how the model directly correlates to your SQL structure is dependent on how you right it. Or which Framework you decide to use. I believe a common one for asp.net is the Microsoft's ASP.Net MVC
Your class cannot be directly mapped to the database without ORM tool, The ORM tool will read your configuration and will map your class to DB row as per your mappings automatically. That means you don't need to read the row and set the class fields explicitly but you have to provide mapping files and have to go through the ORM framework to load the entities, and the framework will take care of the rest
You can check nHibernate and here is getting started on nHibernate.