I have the following (simplified) table
public class Door
{
public int Id { get; set; }
public bool Locked { get; set; }
}
Now the problem with this table is that I don't know how long the door has been locked or not. I could add a new DateTime column, but then, if the door was locked, opened and locked again, I wouldn't know exactly when it was locked the first time since that would be overwritten. So I added a new table
public class Locks
{
public int Id { get; set; }
public int DoorId { get; set; }
public virtual Door Door { get; set; }
public DateTime? LockedFrom { get; set; }
public DateTime? LockedTo { get; set; }
}
and added a public Collection<Locks> to my Door table. This is all nice and good and would solve my first problem. However, Door and Door.Locked has been used extensively throughout our code and changing all those queries would be a very large job. So my hope was that I could rewrite Door.Locked to be a computed column. It should collect the entries for that Door from Locks and compare their DateTimes to the current time to find out if the door is locked right now. It is important that this is a computed column (handled on server side) and not a function or calculated parameter in the entity, since that would cause all queries that filters on Door.Locked to be handled in memory (and I have maaany Doors in my db). I would also prefer if Door.Locked could be not nullable, to avoid changing its type to Bool?, and this seems to be possible by making the column persisted. I've seen examples of computed columns in .NET Core where they use entityTypeBuilder.Property(x => x.Locked).HasComputedColumnSql("some sql formula"), but none that do this when the formula depends upon the content of another table.
Conclusion: I want to create a computed column code first that calculates its value using the content of another table.
Thank you!
Related
I have an mvc5 application that is connected to a EF database. Some fields in this database are meant to be autogenerated as declared in SQL, but when used in MVC and upon inserting records, the GUID only contains the value of 0 for all records. How can I resolve this? Any help will be appreciated. Thanks.
Model class:
public partial class Store
{
public int StoreID { get; set; }
public int CustomerID { get; set; }
public string StoreName { get; set; }
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public System.Guid StoreUID { get; set; }
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int StoreNumber { get; set; }
public string StoreLogo { get; set; }
public string StoreLogoPath { get; set; }
public string StoreAddress { get; set; }
public string StoreCity { get; set; }
public string StoreRegion { get; set; }
public string StoreCountry { get; set; }
public virtual Customer Customer { get; set; }
}
Both StoreUID and StoreNumber supposed to be autogenerated fields. Below is an example how its supposed to be when a new store is inserted, however currently, storeNumber and StoreUID both just return 0.
You need to add defaults to your database table to generate the fields.
ALTER TABLE [dbo].[Store] ADD DEFAULT (newid()) FOR [StoreUID]
ALTER TABLE [dbo].[Store] ADD DEFAULT (myfuncthatreturnsanint()) FOR [StoreNumber]
This isn't really an Entity Framework feature. EF needs to be aware of these column types to generate the appropriate SQL. What you require is something that's actually achieved from the database. For Model First, I got the auto generated int Id functionality by modifying the T4 template that ships with EF to write the appropriate SQL, but it really is database functionality. StoreNumber is a different case since SQL server only allows one identity column.
For your database, your StoreUID column specification should be:
StoreUID uniqueidentifier not null DEFAULT newid()
You don't specify if you're dealing with model first or code first, or if you're building something new, so you may have to modify your existing table for this.
EDIT
If you're using model first, ensure that in your model the Store Generated Column is set to Identity for the StoreUID value to be server generated. If not, and you're not worried about who/what creates the GUID, then create a default constructor for Store, if you don't already have one. Then in there add StoreUID = Guid.NewGuid();.
For StoreNumber, SQL server doesn't support multiple columns with auto incrementing integers. You'd need to research a number of strategies for inserting it.
A number are listed here and here. Essentially make StoreNumber a function of StoreID with Computed Columns, or use an independent Sequence:
ALTER TABLE Store DROP COLUMN StoreNumber;
GO
ALTER TABLE Store ADD StoreNumber AS StoreID + 550000;
Im developing a mvc5 application using CodeFirst approach. Here is the modal class
public class Feeder
{
[Key]
public int FeederId { get; set; }
public string FeederName { get; set; }
public string FeederCode { get; set; }
public DateTime StatusChangeDate { get; set; }
public int CreateBy { get; set; }
public DateTime CreatedDate { get; set; }
public int EditBy { get; set; }
public DateTime EditDate { get; set; }
}
Here for 'FeederCode' i want to generate a string that increments for every record. The string should be like this.
BMK15FEDR00001
Here 'BMK' and 'FEDR' are fixed. But 15(last 2 digits of 2015) will change based on the year. Since this is 2015 it should be 15 and for next year records it's 16. '00001' should increment for every record as 00002, 00003....
I searched for this but couldn't come up with the correct approach. All help appreciated. Thanks!
Why not making it a computed value?
You said that BMK and FEDR are constant, you can extract the year from CreatedDate, and as far as the last part, your FeederId is already set to auto-gen by default so SQL is making that for you.
Now your computed value should be saved as:
`"BMK" + CreatedDate.ToString("yy") + "FEDR" + FeederId;
and this is what you save in the FeederCode value.
Hope that's what you meant.
If u'd also like each year codes to start from 1 again you should set a composite primary key with the other value being the year. and you can also reset the Identity value, you can read here how it's done (part c).
Update regarding the id value:
USE AdventureWorks2012;
GO
DBCC CHECKIDENT ('Person.AddressType', RESEED, 10);
GO
as decirbed in the attached link:
The following example forces the current identity value in the AddressTypeID column in the AddressType table to a value of 10. Because the table has existing rows, the next row inserted will use 11 as the value, that is, the new current increment value defined for the column value plus 1.
If that's not important to you I advice you to just avoid it. if it is you can use it for your needs. the best way to implement this is to trigger a SQL event that each year will reset the auto-identifier.
I'm not sure how to exactly word my question which is probably why I cannot find an example of this anywhere. I'm playing around with MVC4 & EF5 (Web API too) but I'm not sure how to proceed with the Model as I've never really had to do much with them before. I'm doing something around the Periodic Tablet of Elements and I want to make it so that I have a list built for an element with it's electron configuration. However, I'd like to have it just auto number based on the input order. How can I tell EF to auto-increment a field? Basically like a primary key field without that limitation behind it. Here's what I have so far - I'm just not sure how to proceed:
public class Elements
{
public int ElementID { get; set; }
public string Name { get; set; }
public int AtomicNumber { get; set; }
public string Symbol { get; set; }
public virtual Categories Category { get; set; }
public virtual States State { get; set; }
public virtual Occurences Occurence { get; set; }
public virtual ICollection<Configurations> Configuration { get; set; }
}
public class Categories
{
public int CategoryID { get; set; }
public string CategoryName { get; set; }
}
public class States
{
public int StateID { get; set; }
public string StateName { get; set; }
}
public class Occurences
{
public int OccurenceID { get; set; }
public string OccurenceName { get; set; }
}
public class Configurations
{
public int ConfigurationID { get; set; }
public int Order { get; set; }
public int Value { get; set; }
}
Looking above what I'd like is for anytime a value is added to Configurations.Order the value starts at 1 and increases with each new 'row' but only for that specific ElementID.
Does that make sense? I was looking at using Data Annotations but I couldn't find anything that matched other than a Key Field but that'd make each Order a unique number - which I don't want. I feel like I'm not expressing this correctly because of all the stuff I've been looking at to figure it out, so here's a picture! yay!
This very well could be something that is better off from a programmatic standpoint. Even though this data changes once in a blue moon, I wanted to try and do it through EF if possible just so I know how.
Thanks a ton in advance. Also, if you see any other glaring errors, by all means let me know :) I rarely get to work with this side of web dev so I'm sure there's ways to do things better.
How can I tell EF to auto-increment a field?
You can't. Not even for a simple auto-incrementing primary key. Let alone for a field that should increment in relation to other values.
The HasDatabaseGeneratedOption mapping method is not a way to tell EF how to generate key values. It tells EF if and how the database generates values for properties, so EF knows how to respond to that.
So you either have to generate the order numbers in code, or let the database do it (by a trigger, or by mapping CUD actions on Configurations to stored procedures) and tell EF that the database computes the values by HasDatabaseGeneratedOption(DatabaseGeneratedOption.Computed) in the configuration of the Order property.
my user's table in the database is becoming increasingly larger (in terms of columns not rows) and as a consequence is slowing down various areas of my site. This is because it tries to grab every column from the user's table everytime it does a join against it.
I figured i would keep all the common fields in the user's table and then put the additional fields in seperate tables. For example, say i have the following tables in my database:
Users:
- UserID (PK, Identity)
- UserName
- Password
...
UsersActivity:
- UserID (PK, FK)
- LastActivityDate
- LastLoginDate
...
UsersPreferences:
- UserID (PK, FK)
- HtmlEmail
- HideEmail
...
With the following entities:
public class User {
public virtual int UserID { get; set; }
public virtual string UserName { get; set; }
public virtual string Password { get; set; }
public virtual UserActivity Activity { get; set; }
public virtual UserPreferences Preferences { get; set; }
}
public class UserActivity {
public virtual User User { get; set; }
public virtual DateTime LastActivityDate { get; set; }
public virtual DateTime LastLoginDate { get; set; }
}
public class UserPreferences {
public virtual User User { get; set; }
public virtual bool HtmlEmail { get; set; }
public virtual bool HideEmail { get; set; }
}
I was just wondering what is the best way to map this for optimum performance? I figured i could do a one-to-one mapping on the Activity and Performance properties in the User entity. However as far as i understand one-to-one mapping doesn't support lazy loading and this approach would end up being slower.
I also looked into component mapping and wasn't too sure whether i could map this into a seperate table (please correct me if it would be better to keep it in the same table) and whether components supported lazy loading.
Before i go about doing some heavy refactoring of my application i thought i would get the opinion of someone who might have done this. Really appreciate the help.
Thanks
Edit: I found that you could lazy load a one-to-one relationship as long as it is required/constrained. Which it is my case. Therefore i went ahead and carried out the instructions in the following article:
http://brunoreis.com/tech/fluent-nhibernate-hasone-how-implement-one-to-one-relationship/
The trouble now is that i get the error:
NHibernate.Id.IdentifierGenerationException: NHibernate.Id.IdentifierGenerationException: null id generated for: UserActivity.
In NHibernate 3.0 one-to-one relationship supports lazy loading.
And I think that it is better to use Component with combination of Lazy property. Then you will be able to leave all properties in one table and not load them all at once.
You should do some additional application profiling to determine why you're having a performance problem. It's unlikely that it's due to the number of columns in the select list. You probably have an N+1 select problem.
That said, there are many good reasons to use a lightweight object so you might want to look at implementing a DTO (data transfer object) for this.
My entities look something like that (simplified):
public class Person
{
public Guid Id { get; set; }
public string Name { get; set; }
public IList<Department> Departments { get; set; }
}
public class Department
{
public Guid Id { get; set; }
public string Name { get; set; }
}
I'm querying the database through criteria api for all persons that have a department with a certain name that should match a like-pattern.
It happens that a person contains two or more departments whose names contain the same character sequence which is used by the query. Therefore the same person is returned multiple times. To surpress this, I know that I can use criteria.SetResultTransformer(Transformers.DistinctRootEntity); but this works only as long as the result is not paged.
When I'm paging the result I don't only need to get the first page but I also need to know how many entities there are in total. Unfortunately the result transformer does not work when calling criteria.SetProjection(Projections.RowCount()) as there is no result to be transformed.
Can I somehow avoid retrieving the whole list of person with the result transformer and then manually taking the right part out of the collection?
Best Regards
Oliver Hanappi
You need to include distinct in your sql request. Some information you can find here. Second answer mostly