I am working on JDO datanucleus,and I have a list of Objects inside other object as shown below.
User.java
public class User {
#Persistent(primaryKey = "true", valueStrategy = IdGeneratorStrategy.INCREMENT)
long id;
-----
-----
#Persistent(persistenceModifier = PersistenceModifier.PERSISTENT, defaultFetchGroup = "true", mappedBy="user")
#Join
List<Category> categorylist;
-------
}
Category.java
public class Category {
#Persistent(primaryKey = "true", valueStrategy = IdGeneratorStrategy.INCREMENT)
private long id;
------
}
Now as I read on datanucleus site, it is bidirectional relation. Now How do I make a query to access all Users with a having a particular category?
Thanks in advance.
Related
There are many questions about seeding many-to-many relationships in Entity Framework. However, most of them are extremely old, and many-to-many behavior has changed significantly in EFCore5. The official docs recommend overriding OnModelCreating to implement ModelBuilder.Entity<>.HasData().
However, with the new many-to-many behavior (without explicit mappings), I can find no clear path to seed the intermediate tables. To use the example of this tutorial, the BookCategories class is now implicit. Therefore, there is no path to explicitly declare the intermediate table values while seeding.
I've also tried simply assigning the arrays, e.g.,:
public class Book
{
public int BookId { get; set; }
public string Title { get; set; }
public ICollection<Category> Categories { get; set; }
}
public class Category
{
public int CategoryId { get; set; }
public string CategoryName { get; set; }
public ICollection<Book> Books { get; set; }
}
And then at seed time:
Book book = new Book() { BookId = 1, Title = "Brave New World" }
Category category = new Category() { CategoryId = 1, CategoryName = "Dystopian" }
category.Books = new List<Book>() { book };
book.Categories = new List<Category>() { category };
modelBuilder.Entity<Book>().HasData(book);
modelBuilder.Entity<Category>().HasData(category);
... but there are no entries created for BookCategories in the resulting migration. This was somewhat expected, as this article suggests that one must explicitly seed the intermediate table. What I want is something like this:
modelBuilder.Entity<BookCategory>().HasData(
new BookCategory() { BookId = 1, CategoryId = 1 }
);
However, again, since there is no concrete class to describe BookCategories in EFCore5, the only way I can think of to seed the table is to manually edit the migration with additional MigrationBuilder.InsertData commands, which rather defeats the purpose of seeding data via application code.
However, again, since there is no concrete class to describe BookCategories in EFCore5
Actually, as explained in the What's new link, EF Core 5 allows you to have explicit join entity
public class BookCategory
{
public int BookId { get; set; }
public EBook Book { get; set; }
public int CategoryId { get; set; }
public Category Category { get; set; }
}
and configure the many-to-many relationship to use it
modelBuilder.Entity<Book>()
.HasMany(left => left.Categories)
.WithMany(right => right.Books)
.UsingEntity<BookCategory>(
right => right.HasOne(e => e.Category).WithMany(),
left => left.HasOne(e => e.Book).WithMany().HasForeignKey(e => e.BookId),
join => join.ToTable("BookCategories")
);
This way you can use all normal entity operations (query, change tracking, data model seeding etc.) with it
modelBuilder.Entity<BookCategory>().HasData(
new BookCategory() { BookId = 1, CategoryId = 1 }
);
still having the new many-to-many skip navigations mapping.
This is probably the simplest as well as the type-safe approach.
In case you thing it's too much, using the conventional join entity is also possible, but you need to know the shared dictionary entity type name, as well as the two shadow property names. Which as you will see by convention might not be what you expect.
So, by convention the join entity (and table) name is
{LeftEntityName}{RightEntityName}
and the shadow property (and column) names are
{LeftEntityNavigationPropertyName}{RightEntityKeyName}
{RightEntityNavigationPropertyName}{LeftEntityKeyName}
The first question would be - which is the left/right entity? The answer is (not documented yet) - by convention the left entity is the one which name is less in alphabetical order. So with your example Book is left, Category is right, so the join entity and table name would be BookCategory.
It can be changed adding explicit
modelBuilder.Entity<Category>()
.HasMany(left => left.Books)
.WithMany(right => right.Categories);
and now it would be CategoryBook.
In both cases the shadow property (and column) names would be
CategoriesCategoryId
BooksBookId
So neither the table name, nor the property/column names are what you'd normally do.
And apart from the database table/column names, the entity and property names are important because you'd need them for entity operations, including the data seeding in question.
With that being said, even if you don't create explicit join entity, it's better to configure fluently the one created automatically by EF Core convention:
modelBuilder.Entity<Book>()
.HasMany(left => left.Categories)
.WithMany(right => right.Books)
.UsingEntity("BookCategory", typeof(Dictionary<string, object>),
right => right.HasOne(typeof(Category)).WithMany().HasForeignKey("CategoryId"),
left => left.HasOne(typeof(Book)).WithMany().HasForeignKey("BookId"),
join => join.ToTable("BookCategories")
);
Now you can use the entity name to access the EntityTypeBuilder
modelBuilder.Entity("BookCategories")
and you can seed it similar to normal entities with shadow FK properties with anonymous type
modelBuilder.Entity("BookCategory").HasData(
new { BookId = 1, CategoryId = 1 }
);
or for this specific property bag type entity, also with Dictionary<string, object> instances
modelBuilder.Entity("BookCategory").HasData(
new Dictionary<string, object> { ["BookId"] = 1, ["CategoryId"] = 1 }
);
Update:
People seem to misinterpret the aforementioned "extra" steps and find them redundant and "too much", not needed.
I never said they are mandatory. If you know the conventional join entity and property names, go ahead directly to the last step and use anonymous type or Dictionary<string, object>.
I already explained the drawbacks of taking that route - loosing the C# type safety and using "magic" strings out of your control. You have to be smart enough to know the exact EF Core naming conventions and to realize that if you rename class Book to EBook the new join entity/table name will change from "BookCategory" to "CategoryEBook" as well as the order of the PK properties/columns, associated indexes etc.
Regarding the concrete problem with data seeding. If you really want to generalize it (OP attempt in their own answer), at least make it correctly by using the EF Core metadata system rather than reflection and assumptions. For instance, the following will extract these names from the EF Core metadata:
public static void HasJoinData<TFirst, TSecond>(
this ModelBuilder modelBuilder,
params (TFirst First, TSecond Second)[] data)
where TFirst : class where TSecond : class
=> modelBuilder.HasJoinData(data.AsEnumerable());
public static void HasJoinData<TFirst, TSecond>(
this ModelBuilder modelBuilder,
IEnumerable<(TFirst First, TSecond Second)> data)
where TFirst : class where TSecond : class
{
var firstEntityType = modelBuilder.Model.FindEntityType(typeof(TFirst));
var secondEntityType = modelBuilder.Model.FindEntityType(typeof(TSecond));
var firstToSecond = firstEntityType.GetSkipNavigations()
.Single(n => n.TargetEntityType == secondEntityType);
var joinEntityType = firstToSecond.JoinEntityType;
var firstProperty = firstToSecond.ForeignKey.Properties.Single();
var secondProperty = firstToSecond.Inverse.ForeignKey.Properties.Single();
var firstValueGetter = firstToSecond.ForeignKey.PrincipalKey.Properties.Single().GetGetter();
var secondValueGetter = firstToSecond.Inverse.ForeignKey.PrincipalKey.Properties.Single().GetGetter();
var seedData = data.Select(e => (object)new Dictionary<string, object>
{
[firstProperty.Name] = firstValueGetter.GetClrValue(e.First),
[secondProperty.Name] = secondValueGetter.GetClrValue(e.Second),
});
modelBuilder.Entity(joinEntityType.Name).HasData(seedData);
}
Also here you don't need to know which type is "left" and which is "right", neither requires special base class or interface. Just pass sequence of entity pairs and it will properly seed the conventional join entity, e.g. with OP example, both
modelBuilder.HasJoinData((book, category));
and
modelBuilder.HasJoinData((category, book));
would do.
Update (EF Core 5.0.2)
It's working well using the name of the associative table:
builder.Entity("ContractDeclarationType").HasData(
new { ContractsId = 1L, DeclarationTypesId = 1L },
new { ContractsId = 1L, DeclarationTypesId = 2L },
new { ContractsId = 1L, DeclarationTypesId = 3L });
I ended up whipping up a generic solution to this problem based upon the answer from Ivan (thanks!). I'm now able to seed all my M2M tables with this syntax:
// Add book1 and book2 to category1:
modelBuilder.HasM2MData(new [] { book1, book2 }, new [] { category1 });
This may not be fully robust, but it should work with conventional M2M mappings.
It makes some assumptions:
T1 & T2 Inherit from some ModelBase that provides an Id property.
T1 & T2 Have exactly one ICollection<OtherType> property.
You know the correct order (which model is T1 and which is T2) — this can be discovered by running the migration for the tables first and inspecting the migration.
You're running EFCore5 RC2 or later (see this issue).
public static void HasM2MData<T1, T2>
(this ModelBuilder mb, T1[] t1s, T2[] t2s)
where T1 : ModelBase where T2 : ModelBase
{
string table = $"{typeof(T1).Name}{typeof(T2).Name}";
PropertyInfo t1Prop = GetM2MProperty<T1, T2>();
PropertyInfo t2Prop = GetM2MProperty<T2, T1>();
string t1Key = $"{t1Prop.Name}Id";
string t2Key = $"{t2Prop.Name}Id";
foreach (T1 t1 in t1s) {
foreach (T2 t2 in t2s) {
mb.Entity(table).HasData(new Dictionary<string, object>() { [t2Key] = t1.Id, [t1Key] = t2.Id });
}
}
}
// Get a property on T1 which is assignable to type ICollection<T2>, representing the m2m relationship
private static PropertyInfo GetM2MProperty<T1, T2>() {
Type assignableType = typeof(ICollection<T2>);
List<PropertyInfo> props = typeof(T1).GetProperties()
.Where(pi => pi.PropertyType.IsAssignableTo(assignableType))
.ToList();
if (props.Count() != 1) {
throw new SystemException(
$"Expected {typeof(T1)} to have exactly one column of type {assignableType}; got: {props.Count()}");
}
return props.First();
}
In the migration, we see something like:
migrationBuilder.InsertData(
table: "BookCategory",
columns: new[] { "BooksId", "CategoriesId" },
values: new object[,]
{
{ "book1", "category1" },
{ "book2", "category1" }
});
// Create the scoresheet
Scoresheet scoresheet = new Scoresheet();
scoresheet.tsakID = task.ID;
// Query Items to retrieve a list of tasks. Then create a scoresheet
// for each item retrieved and bind them together as foreign keys.
var Items = (from c in db.Items
where c.ID == task.ID
select c).ToList();
// Save scoresheet item to db
scoresheet.ScoresheetItems = new List<ScoresheetItem>();
System.Diagnostics.Debug.WriteLine(scoresheet.ScoresheetID);
for (int i = 0; i < Items.Count(); i++)
{
ScoresheetItem scoresheetItem = new ScoresheetItem();
scoresheetItem.ScoresheetID = scoresheet.ScoresheetID;
scoresheet.ScoresheetItems.Add(scoresheetItem);
}
db.Scoresheets.Add(scoresheet);
db.SaveChanges();
The error is on the line where I am doing scoresheetItem.ScoresheetID = scorehseet.ScoresheetID
The problem is that scoresheet.ScoresheetID is null until it is created. when it is created on the database, the value is assigned as an auto-incrementing value.
How do I get around this so that scoresheet.ScoresheetID is not null so that I can assign it to the scoresheetItem?
Here is the scoresheet model:
public class Scoresheet
{
public int ScoresheetID { get; set; }
public virtual ICollection<ScoresheetItem> ScoresheetItems { get; set; }
}
public class ScoresheetItem
{
public int ScoresheetItemID { get; set; }
public int ScoresheetItemScore { get; set; }
public Nullable<int> ScoresheetID { get; set; }
}
If ScoresheetID is an identity column then you should not be setting it in code at all when creating it. On your object you need to let EF know that is an identity column as well. If this is code first, which I'm assuming, you can either use data annotations
https://msdn.microsoft.com/en-us/library/jj591583(v=vs.113).aspx
or fluent api to configure and map properties
https://msdn.microsoft.com/en-us/library/jj591617(v=vs.113).aspx
When creating child ScoresheetItem(s) you should not set the ScoresheetID either, your models should be configured for the relationship.
Here is one with modeling relationships and navigation properties.
https://msdn.microsoft.com/en-us/library/jj713564(v=vs.113).aspx
Okay, this was actually a pretty simple fault.
There is actually no need at all to set the foreign key such as I was doing right here: scoresheetItem.ScoresheetID = scorehseet.ScoresheetID
When I call scoresheet.ScoresheetItems.Add(scoresheetItem); in the code, it actually handles the foreign key for me.
When I try to index a doc of my defined type, having a list which is supposed to be mapped as a nested-object ("type":"nested"), it's getting mapped as a regular object type.
Take a look at the code:
I've got a simple class like this one:
[ElasticType()]
public class MyJob
{
[ValueFieldAttribute]
public int jobCode { get; set; }
[ValueFieldAttribute(Type = FieldType.nested)]
public IList<JobProfessionalFieldInfo> JobProfessionalFields { get; set; }
}
The code for the JobProfessionalFieldInfo class is:
[ElasticType()]
public class JobProfessionalFieldInfo
{
[ValueFieldAttribute]
public int JobId { get; set; }
[ValueFieldAttribute]
public int CategoryId { get; set; }
}
The code for the ValueFieldAttribute class is:
public class ValueFieldAttribute : ElasticPropertyAttribute
{
public ValueFieldAttribute()
: base()
{
this.Store = false;
this.Index = FieldIndexOption.not_analyzed;
}
}
My program:
static void Main(string[] args)
{
ConnectionSettings node = new ConnectionSettings(new Uri("http://localhost:9200"));
node.SetDefaultIndex("jobs");
ElasticClient client = new ElasticClient(node);
List<JobProfessionalFieldInfo> list = new List<JobProfessionalFieldInfo>();
list.Add(new JobProfessionalFieldInfo { CategoryId = 1, JobId = 1 });
list.Add(new JobProfessionalFieldInfo { CategoryId = 2, JobId = 2 });
var res = client.Index<MyJob>(new MyJob
{
jobCode = 1,
JobProfessionalFields = list
},"jobs", "MyJob",1);
}
Now, when I run it, it indexes the object successfully... BUT(!!) when I get the mapping of the index with GET jobs/MyJob/_mapping, I see that jobProfessionalFields has no "type":"nested" in its mapping.
That results in a query like the following one, returning the indexed doc while it's not supposed to get it back (that's what nested-type is for right?..):
GET jobs/_search
{
"query":
{
"bool":
{
"must":
[
{"match": {"jobId":1}},
{"match": {"categoryId":2}}
]
}
}
}
It's not the end:
I'd a look at here,
there the guy that answered tells that when we use annotations we need to manually call the createIndex and Map methods, but the problem is that I don't have any generic Map method...!
Take a look at here: (just to make you get into the link - here's its start..)
namespace Nest
{
public partial class ElasticClient...
And I don't know how to use the non-generic Map method to put the mapping of my MyJob class.
How can I cause this stuff to map the jobProfessionalFields as nested-type dudes?
Thanks for any help of you guys!
OK, got it LOL!
The MapFromAttributes<> is the right generic method for putting the mapping (at least in the current Nest version I'm using - 0.12.0).
But it demands a manual call for the index creationg, o.w it gives an IndexMissing exception (like the guy in the above mentioned link said).
client.CreateIndex("jobs", new IndexSettings { });
var res = client.MapFromAttributes<MyJob>("jobs","MyJob");
But that's really interesting why isn't it enough to just define the
[ElasticProperty(Type = FieldType.nested)],
in order to get the nested mapping though..
I would be glad to get an answer for that one.
I am new to ASP.NET MVC and I am stuck on a point. I am working on a classified site. My situation is, I have a lot of categories in which a user can post their ads and each ad category have different View. I have created a Controller Action like
public ActionResult PostAd(string CategoryName, string SubCategoryName)
{
if(categoryName == "Vehicle" && SubCategoryName == "Cars")
{
var model = new CarAdViewModel();
// set CarAdViewModel properties...
return View("CarAdCreateView", model);
}
else if(categoryName == "Vehicle" && SubCategoryName == "Bikes")
{
var model = new BikeAdViewModel();
// set BikeAdViewModel properties...
return View("BikeAdViewModel", model);
}
else if(categoryName == "Property" && SubCategoryName == "RentHouse")
{
var model = new RentHouseAdViewModel();
// set RentHouseAdViewModel properties...
return View("RentHouseAdViewModel", model);
}
else................... so on and so on
}
My problem is I have huge number of Categories and Sub Categories almost 60+. And if I keep on coding like above for 60+ categories and subcategories, my PostAd method is going to blast and become unmanageable.
Please tell me some best practice or pattern which can bring me out of this problem.
Unfortunately, some of what you are doing cannot be avoided. There needs to be some form of model and view selection based on category.
Use a factory pattern. Create a base class:
public abstract class BaseCategory
{
public abstract string GetViewName();
public abstract Object CreateModelFromFormData();
}
For each category, create a sub-class derived from BaseCategory and implement the abstract functions.
In your action, do the following:
public ActionResult PostAd(string categoryName, string subCategoryName)
{
BaseFactory factory;
if (categoryName == "Vehicle")
{
if (subCategoryName == "Cars")
{
factory = new CarsFactory();
}
else ...
}
else ...
return View(factory.GetViewName(), factory.CreateModelFromFormData());
}
I have a couple reasons for this schema:
I am purposefully using if/else for the factory selection. Your controller is going to be created and re-created for every action call. So pre-populating a list will constantly and needlessly create objects for categories that will not be selected. A simple if/else will be more efficient. If you want to prevent the if/else, you can put your factories in a Dictionary and select based on the categories, but that would be a lot of needless constructor actions.
I made the CreateModelFromFormData a function because I assume you'll need to copy data from the posted form data. This may require passing in data, but I left the function parameterless.
I used base/derived classes because the copying of the form data will probably need to be custom from the model being created and the form data being posted. Also, saving to persistent storage (file or database) may be category-specific as well.
It would be one of some possible solutions
public class PostAdData
{
public string CategoryName;
public string SubCategoryName;
public string ViewName;
public Type Model;
}
public class PostController : Controller
{
private readonly List<PostAdData> _theData;
public HomeController()
{
_theData = InitializeData();
}
public ActionResult PostAd(string categoryName, string subCategoryName)
{
var data = _theData.FirstOrDefault(c => c.CategoryName == categoryName && c.SubCategoryName == subCategoryName);
if (data != null)
{
var model = Activator.CreateInstance(data.Model);
return View(data.ViewName, model);
}
return View("Error");
}
[NonAction]
public List<PostAdData> InitializeData()
{
var result = new List<PostAdData>
{
new PostAdData
{
CategoryName = "Vehicle",
SubCategoryName = "Cars",
ViewName = "CarAdCreateView",
Model = typeof (CarAdViewModel)
}
};
return result;
}
}
You should make this data driven. You create a lookup table that has a compound primary key of category and subcategory. Then it has a table with View in it. Then you simply ad rows for each category/subcategory/view combination.
If you absolutely don't want a database, then you can use a simple hashset or dictionary.
var views = new Dictionary<Tuple<string,string>,string>();
views.Add(new Tuple<string,string>("Vehicle", "Cars"), "CarAdCreateView");
Then in your PostAd you just lookup the correct view.
What a beautiful solution on www.asp.net to my question, here is the link : http://forums.asp.net/t/1923868.aspx/1?ASP+NET+MVC+Conditional+ViewModel+Abstraction
Edit:
My code is :
public class AdsController : Controller
{
private readonly IAdService _adService;
public AdsController(IAdService adService)
{
_adService = adService;
}
public ActionResult PostAd(string Category, string SubCategory)
{
//Here I will call
var strategy = GetStrategy(CategoryName, SubCategoryName);
strategy.FillModel(_adService );
return View(strategy.ViewName, strategy.Model);
}
}
In my own class-level validator before checking value I want to know are other validators mark it as valid or not?
For instance, before checking that country exists in database I need to ensure that it passes other tests, such as valid length and matches pattern.
How to do this?
To clarify what I really wants, this is real-life example:
#ValidCredentials(groups = AuthAccountForm.FormChecks.class)
public class AuthAccountForm {
#NotEmpty(groups = Login1Checks.class)
#Size.List({
#Size(min = LOGIN_MIN_LENGTH, message = "{value.too-short}", groups = Login2Checks.class),
#Size(max = LOGIN_MAX_LENGTH, message = "{value.too-long}", groups = Login2Checks.class)
})
#Pattern(regexp = LOGIN_REGEXP, message = "{login.invalid}", groups = Login3Checks.class)
private String login;
#NotEmpty(groups = Password1Checks.class)
#Size(min = PASSWORD_MIN_LENGTH, message = "{value.too-short}", groups = Password2Checks.class)
#Pattern(
regexp = PASSWORD_REGEXP,
message = "{password.invalid}",
groups = Password3Checks.class
)
private String password;
#GroupSequence({ Login1Checks.class, Login2Checks.class, Login3Checks.class })
public interface LoginChecks { }
public interface Login1Checks { }
public interface Login2Checks { }
public interface Login3Checks { }
#GroupSequence({ Password1Checks.class, Password2Checks.class, Password3Checks.class })
public interface PasswordChecks { }
public interface Password1Checks { }
public interface Password2Checks { }
public interface Password3Checks { }
public interface FormChecks { }
}
And in controller:
#RequestMapping(method = RequestMethod.POST)
public String processInput(
#Validated({
LoginChecks.class,
PasswordChecks.class,
FormChecks.class
}) final AuthAccountForm form,
final BindingResult result) {
So, now in ValidCredentialsValidator before checks password and login, I need to ensure that them are valid.
I think you should use Groups and Group sequence. In a Group sequence if at least one constraints fails the constraints of the following groups in the sequence get validated. More information are available here.
For example:
#GroupSequence({ Person.class, Group1.class, Group2.class })
class Person {
#Size(min=4, groups=Group1.class)
#Pattern("[a-z]+", groups=Group1.class)
#CheckExistence(groups=Group2.class)
String country;
}
In this example if we validate the Default group, constraints belonging to Person will be validated first then the constraints of Group1 and the constraints of Group2. If one constraints of Group1 is failling the Group2 is not validated.