Code-First Development with Entity Framework

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Tutorial: Get Started with Entity Framework 6 Code First using MVC 5

You will draw your model and workflow will generate your database script. Entity Framework Code first I have created a simple console application to explain that how entity framework works with code first. As explained the above code first approach is the widely accepted and used approach. It helps the developer control the database design and also lets them keep track of the changes. It also maintains version control of the database.

Gaurav Jain Jul 20 Created a console application and in that application, I have installed Nuget package. Once Entity Framework is installed, you can use the built-in class DbContext. Entity framework provide DbContext class to establish connection to database and query the db. Extending DbContext allows to define database model with DbSet.

As shown below, LibraryContext is getting derived from DbContext class. These two classes used with DbSet , Books and Authors represents the tables in database. Meaning these two are the model classes and in DB these will be defined as tables. Define the connection string in config file, Open the package manager console. Use Enable-Migration command as mentioned below. The structure of configuration. It has the constructor of the class and it also has a method Seed. Seed method is generally used to set the master values in the DB.

The next step is to run Add-Migration command from package manager. As it is mentioned in the yellow highlighted text below, when we run Add-Migration command, it will create a. This file contains two methods Up and Down. With the Entity Framework, developers can work at a higher level of abstraction when they deal with data, and can create and maintain data-oriented applications with less code than in traditional applications. The first version of Entity Framework EFv1 was included with.

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NET Framework 3. This version was widely criticized, even attracting a 'vote of no confidence' signed by approximately one thousand developers.

What is Code-First?

The second version of Entity Framework, named Entity Framework 4. NET 4. A third version of Entity Framework, version 4. A refresh of version 4. It includes bug fixes and new supported types. The version 4. Version 5.

Entity Framework Code First Approach - Tutorial

NET framework 4. Also, this version is available for. Net framework 4, but without any runtime advantages over version 4. Version 6. Like ASP. Microsoft then decided to modernize, componentize and bring. Net Core 1. EF Core 1. While EF Core 1. EF Core 2. NET Core 2.


The mapping specification is also expressed in XML. These three files csdl, msl, ssdl can also be created or edited by hand. Entity Data Model Wizard [18] in Visual Studio initially generates a one-to-one mapping between the database schema and the conceptual schema in most of the cases. In the relational schema, the elements are composed of the tables, with the primary and foreign keys gluing the related tables together. In contrast, the Entity Types define the conceptual schema of the data.

The entity types are an aggregation of multiple typed fields — each field maps to a certain column in the database — and can contain information from multiple physical tables. The entity types can be related to each other, independent of the relationships in the physical schema.

Related entities are also exposed similarly — via a field whose name denotes the relation they are participating in and accessing which, instead of retrieving the value from some column in the database, traverses the relationship and returns the entity or a collection of entities it is related with. Entity Types form the class of objects entities conform to, with the Entities being instances of the entity types.

Entities represent individual objects that form a part of the problem being solved by the application and are indexed by a key. For example, converting the physical schema described above, we will have two entity types:. NET Entity Framework performs the joins necessary to have entity reference information from multiple tables, or when a relationship is traversed.

When an entity is updated, it traces back which table the information came from and issues SQL update statements to update the tables in which some data has been updated. Entity types and entity sets just form the logical EDM schema, and can be exposed as anything. NET Entity Framework includes Object Service that presents these entities as Objects with the elements and relationships exposed as properties. Thus Entity objects are just front-end to the instances of the EDM entity types, which lets Object Oriented languages access and use them.

Similarly, other front-ends can be created, which expose the entities via web services e. The identity of an entity is defined by the entity type it is an instance of; in that sense an entity type defines the class an entity belongs to and also defines what properties an entity will have.

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Properties describe some aspect of the entity by giving it a name and a type. The properties of an entity type in ADO. NET Framework. A property can be SimpleType , or ComplexType , and can be multi-valued as well.

All EntityType s belong to some namespace, and have an EntityKey property that uniquely identifies each instance of the entity type. The different property types are distinguished as follows:. All entity instances are housed in EntityContainers, which are per-project containers for entities. Each project has one or more named EntityContainers, which can reference entities across multiple namespaces and entity types. Multiple instances of one entity type can be stored in collections called EntitySets.

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  • One entity type can have multiple EntitySets. EDM primitive types simple types : [20] [22]. Any two entity types can be related, by either an Association relation or a Containment relation. For example, a shipment is billed to a customer is an association whereas an order contains order details is a containment relation. A containment relation can also be used to model inheritance between entities. The relation between two entity types is specified by a Relationship Type , instances of which, called Relationships , relate entity instances. In future releases, other kinds of relationship types such as Composition , or Identification , may be introduced.

    Relationship types are characterized by their degree arity or the count of entity types they relate and their multiplicity. However, in the initial release of ADO. NET Entity Framework, relationships are limited to a binary of degree two bi-directional relationship. Multiplicity defines how many entity instances can be related together. Based on multiplicity, relationships can be either one-to-one, one-to-many, or many-to-many. Relationships between entities are named; the name is called a Role.

    Seeding Data, Reverting Migrations and Creating DB Scripts

    It defines the purpose of the relationship. A relationship type can also have an Operation or Action associated with it, which allows some action to be performed on an entity in the event of an action being performed on a related entity. A relationship can be specified to take an Action when some Operation is done on a related entity. For example, on deleting an entity that forms the part of a relation the OnDelete operation the actions that can be taken are: [23]. For association relationships, which can have different semantics at either ends, different actions can be specified for either end.

    An Enumeration , which defines a map of primitive values and names, is also considered a simple type. Enumerations are supported from framework version 5. ComplexTypes are created from an aggregation of other types. A collection of properties of these types define an Entity Type. This definition can be written in EBNF grammar as:. Facets [24] are used to describe metadata of a property, such as whether it is nullable or has a default value, as also the cardinality of the property, i.