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AndriySvyryd merged 1 commit into dev from InheritanceValidation Apr 1, More TPH validation Changes from all commits Commits. Show all changes. Filter file types. Filter viewed files. Hide viewed files. Clear filters. Jump to file. Failed to load files.Entity, Entity Type, Entity Set - Database Management System
Always Unified Split. For property. GetMapping property.
JPA Implementation Patterns: Mapping Inheritance Hierarchies
For duplicateProperty. GetMapping duplicateProperty. DefaultTypeName ; if! Equals previousTypeStringStringComparison. OrdinalIgnoreCase if! DuplicateColumnName duplicateProperty. Add entityType. RootType ; if root! For entityType ; if annotations. NoDiscriminatorProperty entityType.These strings are exposed publicly for use by database providers and extensions.
It is unusual for application code to need these strings. A second operation started on this context before a previous operation completed. This is usually caused by different threads using the same instance of DbContext. Cannot access a disposed object. A common cause of this error is disposing a context that was resolved from dependency injection and then later trying to use the same context instance elsewhere in your application.
Tutorial: Implement Inheritance with EF in an ASP.NET MVC 5 app
This may occur if you are calling Dispose on the context, or wrapping the context in a using statement. If you are using dependency injection, you should let the dependency injection container take care of disposing context instances.
The convention invocations have reached the recursion limit. This is likely an issue in EF Core, please report it. Data binding directly to 'DbSet. Local' is not supported since it does not provide a stable ordering. ToObservableCollection '. For WinForms bind to 'DbSet. ToBindingList '.
For ASP. ToList ' or use Model Binding. Data binding directly to a store query is not supported.
Hibernate simplifies inheritance mapping
Instead populate a DbSet with data, for example by calling Load on the DbSet, and then bind to local data to avoid sending a query to the database each time the databound control iterates the data. Cannot use multiple DbContext instances within a single query execution. Ensure the query uses a single context instance.
An exception occurred while reading a database value.
See the inner exception for more information. An exception was thrown while attempting to evaluate a LINQ query parameter expression. The block size used for Hi-Lo value generation must be positive. When the Hi-Lo generator is backed by a SQL sequence this means that the sequence increment must be positive.Carlisle cullen x reader lemon
Entity Framework services have not been added to the internal service provider. Either remove the call to UseInternalServiceProvider so that EF will manage its own internal services, or use the method from your database provider to add the required services to the service provider e. No database provider has been configured for this DbContext. A provider can be configured by overriding the DbContext. OnConfiguring method or by using AddDbContext on the application service provider.Sta disassociated from bssid reason 8 sending sta is leaving bss
An attempt was made to use the context while it is being configured. A DbContext instance cannot be used inside OnConfiguring since it is still being configured at this point. This can happen if a second operation is started on this context before a previous operation completed. Any instance members are not guaranteed to be thread safe.Hibernate is a pure Java object-relational mapping and persistence framework that allows you to map plain old Java objects to relational database tables using XML configuration files.
Using Hibernate can save a lot of development time on a project, since the whole JDBC layer is managed by the framework. This means that your application's data access layer will sit above Hibernate and be completely abstracted away from of the underlying data model. Hibernate has a number of advantages over other similar object-relational mapping approaches JDO, entity beans, in-house development, and so on : it's free and open source, it has achieved a good level of maturity, it's widely used, and it has a very active community forum.
To integrate Hibernate into an existing Java project, you'll need to walk through the following steps:. You'll notice that you don't have to modify any Java objects to support the framework. Imagine, for instance, that you needed to somehow change a database table that your Java application used -- by renaming a column, for example. Once you'd changed the table, all you'd have to do to update your Java application would be to update the appropriate XML configuration file.
Entity Framework Core - More than one Discriminator for derived classes
You wouldn't need to recompile any Java code. For those of you who prefer good old-fashioned SQL queries, Hibernate still gives you the opportunity to use them. But our supporting example will use HQL exclusively. HQL is quite simple to use. HQL differs from SQL in that you don't write queries directly on your data model that is, on your tables, columns, etc. Listing 1 illustrates a basic example. The core of Hibernate's functionality resides inside XML configuration files.
We placed them in the config directory of our sample code package which you can download from Related topics. The first file that we'll examine is hibernate. The remaining XML files allow you to map Java classes against database tables. We will take a closer look at those files later, but it is important to know that their filenames follow the pattern ClassName.
In this article, we'll examine a basic example that illustrates how Hibernate works and puts to good use three different strategies under which you can use Hibernate to do your object-relational mapping.
Our example application will be used by an insurance company that must keep legal records of all the property rights that its customers are insured for. We've provided the full source code with this article see Related topics ; this code provides basic functionality from which you could build a full-fledged application, such as a Web or Swing application.
Our example assumes a classic use case for this kind of application. The user would provide the search criteria for any type of customer individual, corporation, government agency, etc.
The user could access a more detailed view of a specific customer from that same list. In our application, a property right is represented by the Right class. A Right can either be a Lease or a Property. A Right is owned by a customer. To represent our customer, we'll use the generic class Person.
A Person can either be an Individual or a Corporation. Of course, the insurance company must know the Estate s to which those Right s are assigned.
An Estate is a very generic term, you'll agree. So, we'll use the Land and Building classes to give our developers more comprehensive objects to work with. View image at full size.Comment 4. A nice comparison of the JPA inheritance mapping options with pictures, and including a description of the MappedSuperclass option, can be found in the DataNucleus documentation. Now the interesting question is: which method works best in what circumstances? Loading entities requires querying only one table, with the discriminator column being used to determine the type of the entity.
This simplicity also helps when manually inspecting or modifying the entities stored in the database. A disadvantage of this strategy is that the single table becomes very large when there are a lot of classes in the hierarchy.
Also, columns that are mapped to a subclass in the hierarchy should be nullablewhich is especially annoying with large inheritance hierarchies. As a result it is also easy to inspect or modify manually. A downside is that polymorphically loading entities requires a UNION of all the mapped tables, which may impact performance. Finally, the duplication of column corresponding to superclass fields causes the database design to not be normalized. This makes it hard to perform aggregate SQL queries on the duplicated columns.
As such this strategy is best suited to wide, but not deep, inheritance hierarchies in which the superclass fields are not ones you want to query on. The JOINED strategy gives you a nicely normalized database schema without any duplicate columns or unwanted nullable columns.
As such it is best suited to large inheritance hierarchies, be the deep or wide. This strategy does make the data harder to inspect or modify manually. Also, the JOIN operation needed to load entities can become a performance problem or a downright barrier to the size of your inheritance strategy. BTW, when using Hibernate proxies, be aware that lazily loading a class mapped with any of the three strategies above always returns a proxy that is an instanceof the superclass.
So to summarize you could say the following rules apply when choosing from JPA's standard inheritance mapping options:. But what if your inheritance hierarchy is very wide or very deep? And what if the classes in your system are modified often? As we found while building a persisted command framework and a flexible CMDB for our Java EE deployment automation product Deployitthe concrete classes at the bottom of a large inheritance hierarchy can change often.
So these two questions often get a positive answer at the same time. Luckily there is one solution to both problems! The first thing to note is that inheritance is a very large component of the object-relational impedance mismatch.
And then question we should ask ourselves is: why are we even mapping all those often changing concrete classes to database tables? If object databases had really broken through, we might be better off storing those classes in such a database.
As it is, relational database have inherited the earth so that is out of the question. It might also be that for a part of your object model the relational model actually makes sense because you want to perform queries and have the database manage the foreign key relations. But for some parts you are actually only interested in simple persistence of objects.
A nice example is the "persisted command framework" I mentioned above. The framework needs to store generic information about each command such as a reference to the "change plan" a kind of execution context it belongs to, start and end times, log output, etc. But it also needs to store a command object that represents the actual work to be done an invocation of wsadmin or wlst or something similar in our case. For the first part the hierarchical model is best suited.
For the second part simple serialization will do. So we first define a simple interface that is implemented by the different command objects in our system:.
And then we create the entity that stores both the metadata the data we want to store in a relational model and the serialized command object:. The serializedCommand field is a byte array that is stored as a blob in the database because of the Lob annotation.In the previous tutorial you handled concurrency exceptions.
This tutorial will show you how to implement inheritance in the data model. In object-oriented programming, you can use inheritance to facilitate code reuse. In this tutorial, you'll change the Instructor and Student classes so that they derive from a Person base class which contains properties such as LastName that are common to both instructors and students.
You won't add or change any web pages, but you'll change some of the code and those changes will be automatically reflected in the database. The Instructor and Student classes in the School data model have several properties that are identical:. Suppose you want to eliminate the redundant code for the properties that are shared by the Instructor and Student entities. Or you want to write a service that can format names without caring whether the name came from an instructor or a student.
You could create a Person base class which contains only those shared properties, then make the Instructor and Student entities inherit from that base class, as shown in the following illustration:. There are several ways this inheritance structure could be represented in the database.
You could have a Person table that includes information about both students and instructors in a single table. Typically, you'd have a discriminator column to indicate which type each row represents. For example, the discriminator column might have "Instructor" for instructors and "Student" for students. This pattern of generating an entity inheritance structure from a single database table is called table-per-hierarchy TPH inheritance.
An alternative is to make the database look more like the inheritance structure. For example, you could have only the name fields in the Person table and have separate Instructor and Student tables with the date fields.
This pattern of making a database table for each entity class is called table per type TPT inheritance. Yet another option is to map all non-abstract types to individual tables.
All properties of a class, including inherited properties, map to columns of the corresponding table. If you implemented TPC inheritance for the PersonStudentand Instructor classes as shown earlier, the Student and Instructor tables would look no different after implementing inheritance than they did before.
This tutorial demonstrates how to implement TPH inheritance. TPH is the default inheritance pattern in the Entity Framework, so all you have to do is create a Person class, change the Instructor and Student classes to derive from Personadd the new class to the DbContextand create a migration.
In the Models folder, create Person. Now update the Instructor. In Instructor. The code will look like the following example:. Make similar changes to Student. The Student class will look like the following example:.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.
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Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Already on GitHub? Sign in to your account. InvalidOperationException: The entity type 'Loan' is part of a hierarchy, but does not have a discriminator property configured.
I found a solution. Apparently, this provider doesn't automatically do registrations for derived classes, so you need to do them manually by overriding the OnModelCreating method in your DbContext -subclass.
Is there a particular reason as to why I need to do this? Shouldn't the provider do this automatically? I took a quick search through the SQLite provider code, as well as through npgsql, and didn't see anything obvious around discriminators.
What is the name of the column that SQLite creates as your discriminator column? The name of the column is simply Discriminator. It was created automatically when I added my initial migration. Ok, that helped a lot in finding where this happens. It seems like something we should use, but I'm a little worried about it causing uenxpected behavior with current systems. I'll try wiring it up, and will bump this library by a minor version, rather than a revision.
If you create a migration for this it should generate just one table called Animal with a Discriminator column. The value of this column can either be AnimalDog or Catwhich would correspond with the type of the model. Instead of generating it it simply throws the exception I posted above aka System.12v dc windshield wiper motor
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New issue. Jump to bottom. Copy link Quote reply. This comment has been minimized. Sign in to view. I'm not sure. Do you know of other providers that don't behave this way?
The SQLite provider didn't behave this way. I haven't tested the other ones. This is the generated migration code for the Loan model: migrationBuilder. MySql 7. Done: 0. I still get the same error as before. InvalidOperationException: The entity type 'Loan' is part of a hierarchy, but does not have a discriminator prope rty configured.
ShowError String message at Microsoft. ValidateInheritanceMapping IModel model You could reproduce this by creating a model that inherits from another one.I need to move this over to EF Core 2. The following code is the closest I can get, but when migrating it fails with the error 'Every concrete entity type in the hierarchy needs to have a unique discriminator value.
Entity Framework Core - More than one Discriminator for derived classes c entity-framework-core entity-framework-core In EF6, the following code achieves the database and model structure that I'm looking for: modelBuilder. Requires "ActivityType". HasValue "Production" ; m. Requires "ActivityStatus". HasValue "Downtime" ; m.
Actual ; modelBuilder. Production ; Please can anyone cast some light on how to have more than one discriminator? Bulk Delete. Bulk Update. Bulk Merge. Popular Answer Well, seems a little odd to need two discriminators - but you could structure it so that Activity has a discriminator and then the sub classes also have their own discriminators alternatively make a complex discriminator modelBuilder. ActivityStatus, x. View more on Stack Overflow. Prime Library. Not affiliated with Stack Overflow.
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