Linq to sql 1 relationship meaning

Configure One-to-One relationship in Code First Entity Framework

linq to sql 1 relationship meaning

Learn how to configure one-to-one relationship using Entity Framework 6.x code first approach. becomes PK & FK in another table in a relational database such as SQL Server. where both ends are required, meaning that the Student entity object must include NET MVC, LINQ, TypeScript, Angular, and More. One-many and one-one relationships using LINQ to SQL.; Author: Shivprasad koirala; Updated: 6 Step 1: Define Entity classes using LINQ. NET Framework 4 covers LINQ to SQL features used to query data. You can define fields that reference existing tables in the database simply by . both sides of a one-to-many relationship described by a foreign key.

ThisKey and OtherKey define which property will define the linkage; for this instance, it is CustomerId. In other words, both the Customer class and the Address class will have a CustomerId property in common. ThisKey defines the name of the property for the Customer class while OtherKey defines the property of the addresses class.

So below is the code snippet which defines the relationship using EntityRef.

One-Many and One-One relationships using LINQ to SQL

All the other properties are same except that we need to define the variable using EntityRef. The first step is to create the data context object with the connection initialized: Please note that we are just firing the query for the customer class. The LINQ engine ensures that all child table data is extracted and placed as per the relationships defined in the entity classes.

Every customer has multiple addresses and every address has a phone object.

  • LINQ to SQL and One-To-Many Relationships
  • Configure One-to-Zero-or-One Relationship in Entity Framework 6
  • How to: Create an association between LINQ to SQL classes (O/R Designer)

Source code We have also attached a source which has the customer, address, and phone tables. The provider must be updated to support the Entity Framework. All you need to do is identify the provider and a database connection string so that the Entity Framework can get to the database. If you need to take advantage of functions or operators that are particular to a database, Entity SQL allows you to do that as well.

Note You may have noticed I use the term data store rather than always referring to the database. It will allow you to use SQL Server, and The providers are being written by the database vendors as well as by third-party vendors. Access and ODBC A provider that supports the Entity Framework needs to have specific knowledge about the type of database it is connecting to.

It needs to be aware of the available functions and operators for the database, as well as the proper syntax for native queries. Open Database Connectivity ODBC providers provide generic access to a variety of databases, including Access, and cannot furnish the necessary database particulars to act as a provider for the Entity Framework. Microsoft does not have plans to build an Access provider because the demand is too low. It also includes a set of design tools for designing the model.

The conceptual data model that the EDM describes is stored in an XML file whose schema identifies the entities and their properties.

Programming Entity Framework by Julia Lerman

Behind the conceptual schema described in the EDM is another pair of schema files that map your data model back to the database. One is an XML file that describes your database and the other is a file that provides the mapping between your conceptual model and the database.

During query execution and command execution for updatesthe Entity Framework figures out how to turn a query or command that is expressed in terms of the data model into one that is expressed in terms of your database. When data is returned from the database, it does the job of shaping the database results into the entities and further materializing objects from those results. It is part of Visual Studio and provides you with a way to work visually with the model rather than tangle with the XML.

Another notable feature of the Designer is that it will let you update the model from the database to add additional database objects that you did not need earlier or that have been added to the database since you created the model. Once you have this first pass at the model, you can begin to customize the model in the Designer. This first release of the Entity Framework is much more focused on creating models from existing databases. Note Frequently, developers ask about the possibility of generating a database from the model.

However, the next version, which will be part of Visual Studiowill include this feature. Object Services provides a class called EntityObject and can manage any class that inherits from EntityObject.

This includes materializing objects from the results of queries against the EDM, keeping track of changes to those objects, managing relationships between objects, and saving changes back to the database. In between querying and updating, Object Services provides a host of capabilities to interact with entity objects, such as automatically working with a lower level of the Entity Framework to do all of the work necessary to make calls to the database and deal with the results.

Object Services also provides serialization both XML and binary. You will see this pattern used in Chapters 20 through The Entity Framework stack Change Tracking Once an entity object has been instantiated, either as a result of data returned from a query or by instantiating a new object in code, Object Services can keep track of that object.

This is the default for objects returned from queries. It constructs Insert, Update, and Delete commands for each object that has been added, modified, or deleted by comparing the original values to the current values of the entity.

If you are using stored procedures in conjunction with entities, it will pass the current values and any original values specifically identified to those procedures. If a SalesPerson has two Orders, there will be one relationship object between the SalesPerson and the first order and another object representing a relationship between the SalesPerson and the second order.

1. Introducing the Entity Framework - Programming Entity Framework [Book]

This paradigm enables the Entity Framework to have a generic way of handling a wide variety of modeling scenarios. Some of the rules of engagement when working with related data are not very intuitive, and you can write code that will raise plenty of exceptions if you break these rules.

linq to sql 1 relationship meaning

Data Binding You can use entity objects in many. In Windows Forms, you can use entities as a data source for data-bound controls or as the data source for BindingSource controls, which orchestrate the binding between objects and UI controls on the form. It provides the functionality necessary for working with the store queries and commands in conjunction with the database provider connecting to the database, executing the commands, retrieving the results from the store, and reshaping the results to match the EDM.

EntityClient is only able to perform queries, and it does this on behalf of Object Services. The difference is that when you work directly with EntityClient, you will get tabular results though the results can be shaped. If you are working with Object Services, it will transform the tabular data created by EntityClient into objects. The tabular data returned by EntityClient is read-only.

Only Object Services provides change tracking and the ability to save changes back to the data store. Here you will learn to write services that are designed more specifically for an enterprise. All of your existing investment will continue to function and you can continue to use this methodology of retrieving data and interacting with it.

The Entity Framework provides a completely different way to retrieve and work with data. You would not integrate the two technologies—for example, using the Entity Framework to query some data, and then pushing it into a data set; there would be no point.

You should use one or the other. As you learn about the Entity Framework, you will find that it provides a very different paradigm for accessing data. You may find that the Entity Framework fits for some projects, but not others where you may want to stick with DataSets. This is what a query with EntityClient returns. Configure a One-to-One relationship using Fluent API We can configure a one-to-One relationship between entities using Fluent API where both ends are required, meaning that the Student entity object must include the StudentAddress entity object and the StudentAddress entity must include the Student entity object in order to save it.

One-Many and One-One relationships using LINQ to SQL - CodeProject

These will always be one-to-zero-or-one relationships. Address makes the Address property of StudentAddress as required and. Student makes the Student property of the StudentAddress entity as required.

Thus it configures both ends as required.

linq to sql 1 relationship meaning

So now, when you try to save the Student entity without the StudentAddress entity without the Student, it will throw an exception.

The entities will appear like the diagram shown below: Learn how to configure a one-to-many relationship in the next section.