Entity Framework Core Part 11 - Relationships
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- čas přidán 3. 12. 2020
- Coding Tutorial: Relational databases use have foreign keys. C# has collections. How can the two be reconciled? (Hint: Use EF Core).
Source code available at: github.com/JasperKent/Entity-... - Věda a technologie
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You can find the source code at github.com/JasperKent/Entity-Framework-Relationships
For more on EF, subscribe at czcams.com/channels/qWQzlUDdllnLmtgfSgYTCA.html
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I was following the tutorial on my local... But EF core showed following error :
Unable to determine the relationship represented by navigation property 'Course.Students' of type 'ICollection'. Either manually configure the relationship, or ignore this property using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.
I am using EF 6 and .net 3.0..
I was required to create A class StudenCources in Code..
learn.microsoft.com/en-us/ef/core/modeling/relationships/many-to-many
Am i missing something?
Thanks
I almost never react on a video. But i'm doing an internship for a company that requires this skillset and your tutorials are one of the best so far. much appreciated!
Glad you're finding them useful.
AMAZING EXPLANATION... I WAS NOT UNDERSTANDING THE DIFFERENCE BETWEEN C# LOGIC AND DATABASE LOGIC TO CREATE RELATIONSHIPS... THIS VIDEO EXPLAIN IT REALLY WELL! THANK YOU!
the instructor explained very clearly .
I've been coming back to this video for the 4th time now. I really appreciate the content of this video. Thanks a lot!
Thank you so much for these tutorials, i'm studying EF at the moment, so the series is right on time!
oh, and yeah, too bad the sound is just as if you sit in an aquarium haha
Yeah - all sorted in later videos, I hope.
Thank you so much from Saudi Arabia
Been a good few years since I was there.
Man, you helped me a lot!
Thank you 🙏
Thanks so much for putting that together. Really appreciated.
Thanks! Helps me a lot.
Great video 🤠
perfect video! thank you so much!
Could you give me a hint, how can one course have multiple editors?
do i need to just replace in DbCOntext from .withOne() to .withMany()?
Do that, plus, change the Course class to have a collection of editors and in the Teacher class, remove the ForeignKey attribute from the CoursesEditted property.
6:30 - when I do that I get an error "The ALTER TABLE statement conflicted with the FOREIGN KEY constraint". Any ideas? I'd like to force a 1-* relationship.
EDIT:
I've removed all the data I had in the database and it solved the issue for me.
Great content! I still have a question though, what about duplicate many-to-many relationships. Let's say that a user can "Like" a post but also can put that post on the "favorite" list, both are many-to-many relationships between user and post how can I create two different tables with that relationship?
Great question! I think you'd have to do this using the Fluent API, something like:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity()
.HasMany(u => u.Likes)
.WithMany(p => p.Users)
.Map(up=>
{
ac.MapLeftKey("User_Id");
ac.MapRightKey("Post_Id");
ac.ToTable("UserPostLikes");
});
modelBuilder.Entity()
.HasMany(u => u.Favourties)
.WithMany(p => p.Users)
.Map(up=>
{
up.MapLeftKey("User_Id");
up.MapRightKey("Post_Id");
up.ToTable("UserPostFavourites");
});
}
@@CodingTutorialsAreGo Thank you so much for your suggestion I will definitely try it :D
I would give this a ten out of ten if you had a microphone that didn't make you sound like you were in a can. I can imagine that if someone was not a native English speaker the echo may make it impossible to understand. Keep up the good work and with this effort it would be worth spending less than $50 for a good mic.
Hi David. I noticed the sound problem on this. I have a Samson C01UPRO, which is usually fine, but for some reason it came out very poor on this recording.
@@CodingTutorialsAreGo Maybe selected the build in mic from the webcam?
@@davidwhite2011 Yeah, I'm thinking maybe something like that. I'll be checking everything more thoroughly in advance next time.
I visit your channel on CZcams regularly to see whats new. even check your Novel reading, that would be great if I know how to contact you
Just email software@jasperkent.com
Sorry sir, if I change the ICollection to List form everyting is gonna be same or should I add different things also ? Thank you from Turkey.
Should still work - give it a try.
Hi, I have a one to one relationship, for example Person and Passport and I want to use the tpt hierarchy, but instead of using the personId in the Passport table I want to use the PassportId in Person table and the Passport table having only his data, could be done in ef core, I imagine that the Passport class won't be have any navigation property, any suggestion?
That's the default behaviour:
public class Person
{
public int Id { get; set; }
public required string Name { get; set; }
public Passport? Passport { get; set; }
}
public class Passport
{
public int Id { get; set; }
public int Number { get; set; }
}
Gives a PassportId on the Person table without any further configuration.
@@CodingTutorialsAreGo In this way I am using the tpt hierarchy and should be the slowest way, database side for me is the best option, the difference between others two types is so relevant from your experience?
Using Entity Framework Core 6.0.5
Just in case someone else got this error "Introducing FOREIGN KEY constraint 'FK_Courses_Teachers_EditorId' on table 'Courses' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
Could not create constraint or index. See previous errors."
To solve it i had to change the code inside the OnModelCreating to:
modelBuilder.Entity().HasOne(c => c.Editor).WithMany(t => t.CoursesEdited).OnDelete(DeleteBehavior.NoAction);
modelBuilder.Entity().HasOne(c => c.Author).WithMany(t => t.CoursesWritten).OnDelete(DeleteBehavior.NoAction);
Hi, I need some help. I followed your tutorial on creating a model extension for an entity. My Employee model has a property that is a many to many entity. For example Employee entity has many Departments so I have an EmployeeDepartment entity. In my Employee model extension I have a property for EmployeeDepartments. I do get the two EmployeeDepartment records but I don't get the EmployeeDepartment property for Department populated. The EmployeeDepartment.Department is null. When I don't use the model extension and just use the entity.Include.thenInclude, the Department is populated. What am I doing wrong?
You'll have to show me some code.
@@CodingTutorialsAreGo I'm so happy you saw and responded. Is there a way I can send you the code and not post it here?
@@KN-hv3gnSorry, I can't really take on private consultancy.
How would you do if both Student and Classroom belong to two different assemblies ? How could you reference both sides? You fall in a Circular Dependencies !!
You're right! You can't have cyclic/reciprocal references across assembly boundaries. The usual fix would be introduce interfaces for both sides to be dependent on. See czcams.com/video/XydkF1AVbYE/video.html
@@CodingTutorialsAreGo Thanks for your replay, I have seen it. But there is also a problem, what will happen if the properties in the separated DLL changed, then the other DLL will not be notified and no error in the compile time, which means the probability of having errors in run-time/production will be high and hidden. That is also a serious problem.
@@katrykonig2466 Once an interface has been published, it should not be changed. However, even if it is changed, the client code will not use the new version until it's explicitly upgraded.
Hi,
I have a Relationship like this:
public class Config
{
[Key]
public int ConfigId { get; set; }
[ForeignKey("temperature_unit_id")]
public TemperatureUnit temperature { get; set; }
public int temperature_unit_id { get; set; }
}
public class TemperatureUnit
{
[Key]
public int TemperatureUnitId { get; set; }
public string name { get; set; }
public string code { get; set; }
}
I want to be able to update the temperature using the Navigational Property temperature like so:
{
id: 1,
temperature:
{
id: 2
}
} // This would be my PUT payload
So let's say that before the POST the temperature_unit_id was 1 and I want to update it with 2.
When I try that though, it asks me for the name and code fields for the temperature. It sounds like it would update the temperature table as well?
I don't want to update the temperature unit fields, I just want to update the reference from 1, to 2.
How would you do this? Do I need to send temperature_unit_id: 2 instead of the temperature object?
Thanks,
Not entirely sure what your asking her, but it looks like your code is attempting to change the TemperatureUnitId (the primary key) of an existing TemperatureUnit object, which you can't do since it is fixed at initialization.
I think what you want to do is change the temperature_unit_id of the Config class, not the TemperatureUnitId of the TemperatureUnit class.
@@CodingTutorialsAreGo sorry I don’t explain more clearly. Correct, I don’t want to update the primary key, I just want to update the temperature_unit_id of the Config class. I am able to do it now by updating temperature_unit_id. I just it could work by sending a different navigational property.
I hade to add OnDelete(DeleteBehavior.Restrict); on the OnModelCreating
so it become
modelBuilder.Entity().HasOne(c => c.Edditer).WithMany(t => t.CoursesEddited).OnDelete(DeleteBehavior.Restrict);
I added this because I had this error
Introducing FOREIGN KEY constraint 'FK_Courses_Teachers_EditterId' on table 'Courses' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
Could not create constraint or index. See previous errors.