Is there any way to preload all nested and sub-nested references with servicestack / ormlite?
public class Person
{
public int Id { get; set; }
[References(typeof(Pants))]
public int PantsId { get; set; }
[Reference]
public Pants Pants { get; set; }
}
public class Pants
{
public int Id { get; set; }
[References(typeof(Pocket))]
public int PocketId { get; set; }
[Reference]
public Pocket Pocket { get; set; }
}
public class Pocket
{
public int Id { get; set; }
public int Depth { get; set; }
}
Db.LoadSelect<Person>()
When I load a person using Db.LoadSelect() it only fetches references up to person.Pants... person.Pants.Pocket is null. I would have to do a Db.LoadReferences(person.Pants) for it to load the pocket reference.
Any way of automatically loading all the nested references, or is it limited to one layer?
Thanks.
OrmLite's db.Load* API's is limited to loading 1-level depth of references. The Db.LoadReferences(instance) can be used to further fetch the disconnected POCO's references.
You should also be mindful if loading references individually to avoid N+1 queries by loading them in a loop, i.e. when possible it's better to use a single query to fetch related records to avoid multiple db hits.
Related
I am trying to create relationship where parent has many children and also includes the oldest child. How to correctly configure that relationship and how to insert the data into the tables?
public class Parent
{
public int Id { get; set; }
public int Name { get; set; }
public int ChildId { get; set; }
public virtual Child Child { get; set; }
public virtual ICollection<Child> Childs { get; set; }
}
public class Child
{
public int Id { get; set; }
public int Age { get; set; }
public int ParentId { get; set; }
public virtual Parent Parent { get; set; }
}
I would recommend against trying to store it as a separate property. Instead, calculate it from existing data with a get-only property something like:
public Child OldestChild => Childs.OrderByDescending(c => c.Age).FirstOrDefault();
If you are concerned about the cost of repeated access, you can look into wrapping the access logic using the Lazy<> class or some other caching methods. If you do, be aware that changes to the Childs collection would then not be reflected in the cached OldestChild result.
FOLLOW-UP: The above is still incomplete as it doesn't resolve cases of children of the same age - close birthdates, twins, adoptees, etc. That also raises the question: Why are are you modeling age (which changes over time vs Birthdate, which is fixed.
I'm struggling to understand the best way to implement some database relationships in EF Core.
Specifically, it involves the navigation properties, where you make a collection in the parent and an object in the child.
Looking at the MS docs here
Relationships, navigation properties, and foreign keys
there is the typical use case presented of a parent child relationship
public class Course
{
public int CourseID { get; set; }
public string Title { get; set; }
public int Credits { get; set; }
public int DepartmentID { get; set; }
public virtual Department Department { get; set; }
}
public class Department
{
public Department()
{
this.Courses = new HashSet<Course>();
}
public int DepartmentID { get; set; }
public string Name { get; set; }
public decimal Budget { get; set; }
public DateTime StartDate { get; set; }
public virtual ICollection<Course> Courses { get; set; }
}
Now this is fine for the above use case.
However, I am working on a specification system for process recipes. There are lots of machines, materials, areas, buildings and other things involved.
One of the tables in the database is "Unit", as in unit of measurement - that is kg, m, cm, etc.
This table is used as a lookup in many tables in the database, at least 20.
As such, if I've understood the recommended approach, I would end up with
pubic class Unit
{
public Guid Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Recipes> Recipes{ get; set; }
public virtual ICollection<Coll2> Coll2{ get; set; }
public virtual ICollection<Coll3> Coll2{ get; set; }
public virtual ICollection<Coll4> Coll2{ get; set; }
public virtual ICollection<Coll5> Coll2{ get; set; }
public virtual ICollection<Coll..n> Coll..n{ get; set; }
}
This applies not just for unit, but also for quite a few other generic lookup items, such as a warehouse. There are many entities that use a link to the warehouse.
What is the correct approach when using this kind of lookup?
I'm sorry if things aren't clear, hopefully they are.
I’m coming from an intermediate C++ background (and to a lesser extent, C#) and wanted to try to build a project in Asp.net MVC 6 with EF 7 – not realizing how completely different it is from simple C# forms. I’ve stumbled through and researched a lot but since I’m a total noob I’m stumped at this point.
I have the following models:
public class Shift
{
public int ShiftId { get; set; }
//other properties
public virtual ICollection<ShiftActivity> ShiftActivity { get; set;}
}
public class ShiftActivity
{
public int ShiftActivityID { get; set; }
public DateTime StartTime { get; set; }
public int ShiftID { get; set; }
public int ActivityID { get; set; }
public int LocationID { get; set; }
public virtual Shift Shift { get; set; }
public virtual Activity Activity { get; set; }
public virtual Location Location { get; set; }
}
public class Activity
{
public int ActivityID { get; set; }
public string ActivityName { get; set; }
public virtual ICollection<ShiftActivity> ShiftActivity { get; set; }
}
public class Location
{
public int LocationID { get; set; }
public string LocationName { get; set; }
public string LocationAddress { get; set; }
public int locationZip { get; set; }
public virtual ICollection<ShiftActivity> ShiftActivity { get; set; }
}
I would like to create a shift and be able to input all the required fields all from one view. For instance, when I create the shift, I need to pick the type of location and activity to add to the ShiftActivity table which is then updated. Eventually I would like to be able to dynamically add additional activities (I’m assuming I’ll need javascript for that), but that’s another issue. I know I need a viewmodel to access all the tables, but I’m unclear as to how the viewmodel should be structured correctly.
Also, can the ShiftController update the ShiftActivity table directly or do I need to transfer the data somehow to the ShiftAcitivityController when the form is submitted? Either way, can someone point me to an example? Thank you… Any help is greatly appreciated.
First of all ASP.NET and MVC 4 are very new to me (+- one month) and sorry if its a bad question.
I've got two classes "Turma" and "Curso"
public class Turma
{
[Key]
public int idCurso { get; set; }
public string RefTurma { get; set; }
public Curso Curso { get; set; }
public string NomeCurso { get; set; }
}
and
public class Curso
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.None)]
public int idArtigoAT { get; set; }
public string ConteudoPrograma { get; set; }
public virtual ICollection<Turma> Turmas { get; set; }
}
After this I started a migration and updated the database. So far so good, but then problems.
Due to new information the primary key type should be varchar(18). I've tried to change but so far without success.
Any ideia or solution???
No, what you want is an 'Id' property and an 'MyCustomUniqueName' property. this custom property, should be and unique index in database. this is the best design for this situation IMHO.
I've got 2 entities:
public class School
{
public int Id { get; set; }
...
public virtual ICollection<Seminar> Seminars { get; set; }
}
public class Seminar
{
public int Id { get; set; }
...
public virtual ICollection<School> Schools { get; set; }
public virtual ICollection<Price> Prices { get; set; } // wrong??
}
public class Price
{
public int Id { get; set; }
public decimal Value { get; set; }
public virtual School School { get; set; }
public virtual Seminar Seminar { get; set; }
}
How to map "Price" property for getting something like this:
var priceOfSomeSeminar = someSchool.Seminars[0].Price
Is it possible? So I think I need help with the Fluent API modelBuilder relationship establishment...
Well, ICollection doesn't have an indexer, so you can't use array syntax with it. You can, however, convert it to an IEnumerable and then convert that to a List, which can then be indexed.
But no, you are using the correct semantics, so this should just work. No need to work with the fluent api.
I think you have an error though, Price should not have a School member. There is no direct relationship between price and school.