I have an EF Core model that has a binary field
class SomeModel {
string Id;
string otherProperty;
byte[] blob;
};
Usually, when I query the DB, I want to return a list of this Model - and then, on subsequent calls, query just a single entity, but return the blob.
I can't see a way in either data or code first to prevent EF Core paying the cost of retrieving the blob field always.
I really want to be able to say something like:
var list = await Context.SomeModels.ToListAsync();
// later
var item = await Context.SomeModels
.Where(m=>m.Id==someId)
.Include(m=>m.blob)
.FirstOrDefaultAsync();
I think I might have to put the blobs into a 2nd table so I can force a optional join.
The only way you could get a separate loading is to move the data to a separate entity with one-to-one relationship.
It doesn't need to be a separate table though. Although the most natural choice looks to be owned entity, since owned entities are always loaded with the owners, it has to be a regular entity, but configured with table splitting - in simple words, share the same table with the principal entity.
Applying it to your sample:
Model:
public class SomeModel
{
public string Id { get; set; }
public string OtherProperty { get; set; }
public SomeModelBlob Blob { get; set; }
};
public class SomeModelBlob
{
public string Id { get; set; }
public byte[] Data { get; set; }
}
Configuration:
modelBuilder.Entity<SomeModelBlob>(builder =>
{
builder.HasOne<SomeModel>().WithOne(e => e.Blob)
.HasForeignKey<SomeModelBlob>(e => e.Id);
builder.Property(e => e.Data).HasColumnName("Blob");
builder.ToTable(modelBuilder.Entity<SomeModel>().Metadata.Relational().TableName);
});
Usage:
Code:
var test = context.Set<SomeModel>().ToList();
SQL:
SELECT [s].[Id], [s].[OtherProperty]
FROM [SomeModel] AS [s]
Code:
var test = context.Set<SomeModel>().Include(e => e.Blob).ToList();
SQL:
SELECT [e].[Id], [e].[OtherProperty], [e].[Id], [e].[Blob]
FROM [SomeModel] AS [e]
(the second e.Id in the select looks strange, but I guess we can live with that)
Related
My database has a table like this:
Cats
- CatId INT PK
- Name VARCHAR(100)
- FavoriteToy VARCHAR(100)
And my code looks like this:
Cat.cs
public int CatId { get; set; }
public string Name { get; set; }
public Toy FavoriteToy {get; set; }
StaticVariables.cs
public enum Toy { Box, Ball, StuffedAnimal }
In a normalized database I would use a lookup table in the database to store all the toys and then the Cats table would just store a ToyId. But for this situation it's a lot easier to just store the FavoriteToy as a string even though it will be redundant.
The problem is I don't know how to convert a string in the database to an enum in code without creating a second FavoriteToyString property and having FavoriteToy just be a computed that returns the enum derived from FavoriteToyString.
I've heard this might be possible in the current version of entity framework. Is that true? Can you please show me how to do this?
You may use DTO class and automapper to solve your issue :)
Generally, yes a lookup table reference is a better option since your data can comply with referential integrity. That is, No cat records with toys that your Enum hopefully doesn't contain. (Though your Enum would need to be kept in sync with the Toys table.) You can configure EF to store enumerations as a string using a bit of a trick with the mapping:
public class Cat
{
[Key]
public int CatId { get; set; }
public string Name { get; set; }
[Column("FavoriteToy")]
public string FavoriteToyMapped { get; set; }
[NotMapped]
public Toy FavoriteToy
{
get { return (Toy)Enum.Parse(typeof(Toy), FavoriteToyMapped); }
set { FavoriteToyMapped = value.ToString(); }
}
}
The caveat of this approach is that where you might use Linq to Entity to filter on your cat's favorite toy, you need to reference the FavoriteToyMapped value in the query expression because EF/DB won't know what FavoriteToy is.
I.e.
Cats with a favorite toy of "Yarn"
var catsThatLoveYarn = context.Cats.Where(c => c.FavoriteToyMapped == Toys.Yarn.ToString()).ToList();
// not
var catsThatLoveYarn = context.Cats.Where(c => c.FavoriteToy == Toys.Yarn).ToList();
// Will error because EF doesn't map that property.
Once you are working with instances of entities, that the set of entities has been pulled back from the database, you can further access/refine queries with FavoriteToy. Just be cautious and prepared for the unknown field if you use it too early and EF goes and tries to compose a query.
var threeYearOldCats = context.Cats.Where(c => c.Age == 3).ToList();
var threeYearOldCatsThatLoveYarn = threeYearOldCats.Where(c => c.FavoriteToy == Toys.Yarn).ToList();
This is Ok because the .ToList() in the first query executed the EF-to-SQL, so threeYearOldCats is now a local List<Cat> of cat entities, not an IQueryable<Cat>.
I have a database first model.
My application UI provides a group of checkboxes, one for each value in Data_Type.
When the user checks one, I expect a row to be added in BUS_APPL_DATA_TYPE,
however I'm getting an error about Cannot insert explicit value for identity column in DATA_TYPE (And I absolutely do not actually want to insert data in this table)
My EF Model class for BUS_APPL has this property
public ICollection<BusApplDataType> BusApplDataType { get; set; }
And that EF Model class looks like
public partial class BusApplDataType
{
public int BusApplId { get; set; }
public int DataTypeId { get; set; }
[Newtonsoft.Json.JsonIgnore]
public BusAppl BusAppl { get; set; }
public DataType DataType { get; set; }
}
What exactly do I need to add to the BusApplDataType collection to get a record to be inserted in BUS_APPL_DATA_TYPE?
Edit:
At a breakpoint right before SaveChanges.
The item at index 2 is an existing one and causes no issues.
The item at index 3 is new. Without this everything updates fine. There is a DATA_TYPE with id 5 in the database.
The surrounding code, if it helps.
[HttpPut("{id}")]
public IActionResult Update(int id, [FromBody] BusAppl item)
{
...
var existing = _context.BusAppl.FirstOrDefault(t => t.Id == id);
...
existing.BusApplDataType = item.BusApplDataType; //A bunch of lines like this, only this one causes any issue.
...
_context.BusAppl.Update(existing);
_context.SaveChanges();
return new NoContentResult();
}
My issue was that I needed to use my context to look up the actual entity, using info passed, instead of using the one with all the same values that was passed into my api directly.
I'm trying to fetch (in disconnected way) an entity with its all related entities and then trying to update the entity. But I'm getting the following error:
Attaching an entity of type 'Feature' failed because another entity of the same type already has the same primary key value.
public class Person
{
public int PersonId { get; set; }
public string Personname { get; set }
public ICollection Addresses { get; set; }
}
public class Address
{
public int AddressId { get; set; }
public int PersonId { get; set; }
public string Line1 { get; set; }
public string City { get; set; }
public string State { get; set; }
public Person Person { get; set; }
public ICollection<Feature> Features { get; set; }
}
// Many to Many: Represented in database as AddressFeature (e.g Air Conditioning, Central Heating; User could select multiple features of a single address)
public class Feature
{
public int FeatureId { get; set; }
public string Featurename { get; set; }
public ICollection<Address> Addresses { get; set; } // Many-To-Many with Addresses
}
public Person GetCandidate(int id)
{
using (MyDbContext dbContext = new MyDbContext())
{
var person = dbContext.People.AsNoTracking().Where(x => x.PersonId == id);
person = person.Include(prop => prop.Addresses.Select(x => x.Country)).Include(prop => prop.Addresses.Select(x => x.Features));
return person.FirstOrDefault();
}
}
public void UpdateCandidate(Person newPerson)
{
Person existingPerson = GetPerson(person.Id); // Loading the existing candidate from database with ASNOTRACKING
dbContext.People.Attach(existingPerson); // This line is giving error
.....
.....
.....
}
Error:
Additional information: Attaching an entity of type 'Feature' failed because another entity of the same type already has the same primary key value.
It seems like (I may be wrong) GetCandidate is assigning every Feature within Person.Addresses a new instance. So, how could I modify the GetCandidate to make sure that the same instance (for same values) is bing assisgned to Person.Addresses --> Features.
Kindly suggest.
It seems like (I may be wrong) GetCandidate is assigning every Feature within Person.Addresses a new instance. So, how could I modify the GetCandidate to make sure that the same instance (for same values) is bing assisgned to Person.Addresses --> Features.
Since you are using a short lived DbContext for retrieving the data, all you need is to remove AsNoTracking(), thus allowing EF to use the context cache and consolidate the Feature entities. EF tracking serves different purposes. One is to allow consolidating the entity instances with the same PK which you are interested in this case, and the second is to detect the modifications in case you modify the entities and call SaveChanges(), which apparently you are not interested when using the context simply to retrieve the data. When you disable the tracking for a query, EF cannot use the cache, thus generates separate object instances.
What you really not want is to let EF create proxies which hold reference to the context used to obtain them and will cause issues when trying to attach to another context. I don't see virtual navigation properties in your models, so most likely EF will not create proxies, but in order to be absolutely sure, I would turn ProxyCreationEnabled off:
public Person GetCandidate(int id)
{
using (MyDbContext dbContext = new MyDbContext())
{
dbContext.Configuration.ProxyCreationEnabled = false;
var person = dbContext.People.Where(x => x.PersonId == id);
person = person.Include(prop => prop.Addresses.Select(x => x.Country)).Include(prop => prop.Addresses.Select(x => x.Features));
return person.FirstOrDefault();
}
}
How to configure a EF6 migration with a model class having?
A collection o items
A navigation property to one particular item
public class MyModel
{
[Key]
public int Id { get; set; }
// My collection of elements
public virtual ICollection<MyCollectionElement> MyCollection { get; set; }
// Optional navigation to a particular element from the collection
[ForeignKey("CurrentElement")]
public int? CurrentElementId { get; set; }
public virtual MyCollectionElement CurrentElement { get; set; }
}
public class MyCollectionElement
{
[Key]
public int Id { get; set; }
// Required navigation to MyClass
[ForeignKey("MyModel")]
public int MyModelID { get; set; }
public virtual MyModel Model { get; set; }
}
Configuration
modelBuilder.Entity<MyModel>()
.HasMany(x => x.MyCollection)
.WithRequired(x => x.Model)
.HasForeignKey(x => x.MyModelID)
.WillCascadadeOnDelete(false);
Throws several errors on Update-Database, like
Unable to determine a valid ordering for dependent operations.
I would like a solution which doesn't involve a boolean IsCurrent in MyCollectionElement to make another query later and find which element is the current; instead, I would like to store the current element's id with my model, like exposed.
Also, I don't mind making int CurrentElementId non nullable (required) if it's easier.
Thanks.
This chicken-and-egg problem always looms when there are circular relationships. The error...
Unable to determine a valid ordering for dependent operations.
...is not thrown when the database is created. The database can be created just fine. It occurs when you try to insert a MyModel record and a MyCollectionElement referring to one another in the same unit of work. In the Seed method you probably have something like
var element = new MyCollectionElement();
var model = new MyModel();
model.MyCollection.Add(element);
model.CurrentElement = element;
The statement model.MyCollection.Add(element); requires model to be inserted first, so element can refer to it in its foreign key. But model.CurrentElement = element; requires element to be inserted first.
You can only avoid this situation by calling SaveChanges twice, and wrapping everything in a TransactionScope if you want the assignments to be transactional:
using(var ts = new TransactionScope())
{
using(var db = new MyContext()
{
var element = new MyCollectionElement();
var model = new MyModel();
model.MyCollection.Add(element);
db.MyModels.Add(model);
db.SaveChanges();
model.CurrentElement = element;
db.SaveChanges();
}
ts.Complete();
}
This also means that int CurrentElementId should remain nullable.
Got a very difficult EntityFramework Code First question. I'll keep this as simple as possible.
Imagine we have n number of classes, lets start with 2 for now
public class Person
{
public string Name { get; set; }
}
public class Address
{
public string AddressLine1 { get; set; }
public string AddressLine2 { get; set; }
}
Now then, what I want to do is be able to search the domain model with a single string, i.e. something like DbContext.Search( "Foo" ). The call would search both the person and address tables for a string match and would return a list populated with both Person and Address entities.
Have to say I am not entirely clear how to go about it but I am considering using DataAnnotations to do something like this
public class Person
{
**[Searchable]**
public string Name { get; set; }
}
public class Address
{
**[Searchable]**
public string AddressLine1 { get; set; }
**[Searchable]**
public string AddressLine2 { get; set; }
}
Am I on the right track?
Should I use the Fluent API instead?
Reflection?
Any and all thoughts massively appreciated.
the Find method searches only in the Primary Key column. If we don't make any column explicitly primary key column then find method will throw error. Generally EF convention takes propertyName+id as the primary key in the class. But if you want to search with Name then Make add [Key] to the property. it will become primary key and u will be able to find properties.
dbContext.Addresses.find("Foo");
Create a new object type onto which you'll project 2 types of search results:
public class Result
{
public string MainField { get; set; }
// you may have other properties in here.
}
Then find entities of each type that match your criteria, projecting them onto this type:
var personResults = DbContext.Persons
.Where(p => p.Name == "Foo")
.Select(p => new Result{MainField = p.Name});
// don't forget to map to any other properties you have in Result as well
var addressResults = DbContext.Adresses
.Where(a =>
a.AddressLine1 == "Foo" ||
a.AddressLine2 == "Foo"
).
.Select(a => new Result{MainField = a.AddressLine1 + ", " + a.AddressLine2 });
// again, don't forget to map to any other properties in Result
Then merge the lists:
var allResults = personResults.Union(addressResults).ToList();
...at which point you can sort the list however you like.
"Result" and "MainField", are rather generic; just using them because I am not thoroughly aware of your domain model.