Entity Framework

Entity Framework
Original author(s)Microsoft
Developer(s).NET Foundation
Initial releaseAugust 11, 2008; 13 years ago (2008-08-11)
Stable release
Entity Framework 6: v6.4.4
Entity Framework Core: v5.0.0 / Entity Framework 6: April 22, 2020; 19 months ago (2020-04-22)[1]
Entity Framework Core: October 24, 2020; 13 months ago (2020-10-24)[2]
Repositorygithub.com/dotnet/ef6
github.com/dotnet/efcore
Written inC#
Platform.NET Framework,
.NET Core
TypeObject–relational mapping
LicenseApache License 2.0
Websitemsdn.microsoft.com/en-us/data/ef.aspx

Entity Framework (EF) is an open source[3] object–relational mapping (ORM) framework for ADO.NET. It was originally shipped as an integral part of .NET Framework. Starting with Entity Framework version 6, it has been delivered separately from the .NET Framework.[citation needed]

Overview[]

The Entity Framework is a set of technologies in ADO.NET that supports the development of data-oriented software applications. Architects and developers of data-oriented applications have typically struggled with the need to achieve two very different objectives. They must model the entities, relationships, and logic of the business problems they are solving, and they must also work with the data engines used to store and retrieve the data. The data can span multiple storage systems, each with its own protocols; even applications that work with a single storage system must balance the requirements of the storage system against the requirements of writing efficient and maintainable application code. This problem is generally referred to as the "object–relational impedance mismatch".[citation needed]

Many object–relational mapping (ORM) tools (aka "object–relational managers") have been developed to enable developers to work with data in the form of domain-specific objects and properties, such as customers and customer addresses, without having to concern themselves with the underlying database tables and columns where this data is stored. With an ORM, 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. Entity Framework is the ORM solution currently promoted for use within the Microsoft development stack.[4]

History[]

The first version of Entity Framework (EFv1) was included with .NET Framework 3.5 Service Pack 1 and Visual Studio 2008 Service Pack 1, released on 11 August 2008 (13 years ago) (2008-08-11). This version was widely criticized, even attracting a 'vote of no confidence' signed by at least one thousand developers.[5]

The second version of Entity Framework, named Entity Framework 4.0 (EFv4), was released as part of .NET 4.0 on 12 April 2010 and addressed many of the criticisms made of version 1.[6]

A third version of Entity Framework, version 4.1, was released on April 12, 2011, with Code First support.

A refresh of version 4.1, named Entity Framework 4.1 Update 1, was released on July 25, 2011. It includes bug fixes and new supported types.

The version 4.3.1 was released on February 29, 2012.[7] There were a few updates, like support for migration.

Version 5.0.0 was released on August 11, 2012[8] and is targeted at .NET framework 4.5. Also, this version is available for .Net framework 4, but without any runtime advantages over version 4.

Version 6.0 was released on October 17, 2013[9] and is now an open source project licensed under Apache License v2. Like ASP.NET MVC, its source code is hosted at GitHub using Git.[10] This version has a number of improvements for code-first support.[11]

Microsoft then decided to modernize, componentize and bring .NET cross-platform to Linux, OSX and elsewhere, meaning the next version of Entity Framework would be a complete rewrite.[12] On 27 June 2016 this was released as Entity Framework Core 1.0, alongside ASP.NET Core 1.0 and .NET Core 1.0.[13] It was originally named Entity Framework 7, but was renamed to highlight that it was a complete rewrite rather than an incremental upgrade and it doesn't replace EF6.[14]

Entity Framework Core 1.0 is licensed under Apache License v2, and is being built entirely in the open on GitHub. While Entity Framework Core 1.0 shares some conceptual similarities with prior versions of Entity Framework, it is a completely new codebase designed to be more efficient, powerful, flexible, and extensible, will run on Windows, Linux and OSX, and will support a new range of relational and NOSQL data stores.[12]

Entity Framework Core 2.0 was released on 14 August 2017 (4 years ago) (2017-08-14) along with Visual Studio 2017 15.3 and ASP.NET Core 2.0 [15]

Entity Framework Core 3.0 was released on 23 September 2019 (2 years ago) (2019-09-23) along with Visual Studio 2019 16.3 and ASP.NET Core 3.0, [16]

Entity Framework Core 3.1 (EF Core 3.1) was formally released for production use on 3 December 2019 (23 months ago) (2019-12-03) and will be the preferred long-term supported version until at least 3 December 2022.[17][18]

Entity Framework Core 5.0.2 (EF Core 5) was released for production use on 12 January 2021 (10 months ago) (2021-01-12).[19][20]

The most recent Entity Framework Core 6.0 (EF Core 6) was released on November 10, 2021. [21][22]

Architecture[]

ADO.NET Entity Framework stack.

The architecture of the ADO.NET Entity Framework, from the bottom up, consists of the following:[citation needed]

Entity Data Model[]

The Entity Data Model (EDM) specifies the conceptual model (CSDL) of the data, using a modelling technique that is itself called Entity Data Model, an extended version of the entity–relationship model.[23] The data model primarily describes the Entities and the Associations they participate in. The EDM schema is expressed in the Schema Definition Language (SDL), which is an application of XML (Extended markup language). In addition, the mapping (MSL) of the elements of the conceptual schema (CSDL) to the storage schema (SSDL) must also be specified. The mapping specification is also expressed in XML.[24]

Visual Studio also provides the Entity Designer for visual creation of the EDM and the mapping specification. The output of the tool is the XML file (*.edmx) specifying the schema and the mapping. Edmx file contains EF metadata artifacts (CSDL/MSL/SSDL content). These three files (csdl, msl, ssdl) can also be created or ed by hand.[citation needed]

Mapping[]

Entity Data Model Wizard[25] in Visual Studio initially generates a one-to-one (1:1) 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.[citation needed]

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) with which it is related.[citation needed]

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:

The logical schema and its mapping with the physical schema is represented as an Entity Data Model (EDM), specified as an XML file. ADO.NET Entity Framework uses the EDM to actually perform the mapping letting the application work with the entities, while internally abstracting the use of ADO.NET constructs like DataSet and RecordSet. ADO.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. ADO.NET Entity Framework uses eSQL, a derivative of SQL, to perform queries, set-theoretic operations, and updates on entities and their relationships. Queries in eSQL, if required, are then translated to the native SQL flavor of the underlying database.[citation needed]

Entity types and entity sets just form the logical EDM schema, and can be exposed as anything. ADO.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.g., WCF Data Services) or XML that is used when entities are serialized for persistence storage or over-the-wire transfer.[26]

Entities[]

Entities** are instances of EntityTypes; they represent the individual instances of the objects (such as customer, orders) to which the information pertains. 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. Properties describe some aspect of the entity by giving it a name and a type. The properties of an entity type in ADO.NET Entity Framework are fully typed, and are fully compatible with the type system used in a DBMS system, as well as the Common Type System of the .NET Framework. A property can be SimpleType, or ComplexType, and can be multi-valued as well. All EntityTypes 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:[citation needed]

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. One entity type can have multiple EntitySets.[citation needed]

EDM primitive types (simple types):[27][29]

EDM type CLR type mapping
Edm.Binary Byte[]
Edm.Boolean Boolean
Edm.Byte Byte
Edm.DateTime DateTime
Edm.DateTimeOffset DateTimeOffset
Edm.Decimal Decimal
Edm.Double Double
Edm.Guid Guid
Edm.Int16 Int16
Edm.Int32 Int32
Edm.Int64 Int64
Edm.SByte SByte
Edm.Single Single
Edm.String String
Edm.Time TimeSpan

Relationships[]

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.[citation needed]

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. It defines the purpose of the relationship.[citation needed]

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:[30]

For association relationships, which can have different semantics at either ends, different actions can be specified for either end.[citation needed]

Schema definition language[]

ADO.NET Entity Framework uses an XML based Data Definition Language called Schema Definition Language (SDL) to define the EDM Schema. The SDL defines the SimpleTypes similar to the CTS primitive types, including String, Int32, Double, Decimal, Guid, and DateTime, among others. An Enumeration, which defines a map of primitive values and names, is also considered a simple type. Enumerations are supported from framework version 5.0 onwards only. 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:[citation needed]

  EntityType ::= 
    ENTITYTYPE entityTypeName [BASE entityTypeName]
      [ABSTRACT true|false] KEY propertyName [, propertyName]*
      {(propertyName PropertyType [PropertyFacet]*) +}

  PropertyType ::= (
        (PrimitiveType [PrimitiveTypeFacets]*)
        | (complexTypeName)
        | RowType
    
      PropertyFacet ::= (
        [NULLABLE true | false]
        | [DEFAULT defaultVal] 
        | [MULTIPLICITY [1|*]]
      )
    
      PropertyTypeFacet ::= 
        MAXLENGTH | PRECISION | SCALE 
        | UNICODE | FIXEDLENGTH | COLLATION
        | DATETIMEKIND | PRESERVESECONDS
    
      PrimitiveType ::= 
        BINARY | STRING | BOOLEAN
        | SINGLE | DOUBLE | DECIMAL | GUID
        | BYTE | SBYTE | INT16 | INT32 | INT64
        | DATETIME | DATETIMEOFFSET | TIME
  )

Facets 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.e., whether the property is single valued or multi valued. A multiplicity of “1” denotes a single valued property; a “*” means it is a multi-valued property. As an example, an entity can be denoted in SDL as:[31]

<ComplexType Name="Addr">
    <Property Name="Street" Type="String" Nullable="false" />
    <Property Name="City" Type="String" Nullable="false" />
    <Property Name="Country" Type="String" Nullable="false" />
    <Property Name="PostalCode" Type="Int32" />
</ComplexType>
<EntityType Name="Customer">
    <Key>
        <PropertyRef Name="Email" />
    </Key>
    <Property Name="Name" Type="String" />
    <Property Name="Email" Type="String" Nullable="false" />
    <Property Name="Address" Type="Addr" />
</EntityType>

A relationship type is defined as specifying the end points and their multiplicities. For example, a one-to-many relationship between Customer and Orders can be defined as

<Association Name="CustomerAndOrders">
    <End Type="Customer" Multiplicity="1" />
    <End Type="Orders" Multiplicity="*">
        <OnDelete Action="Cascade" />
    </End>
</Association>

Querying data[]

Entity SQL[]

ADO.NET Entity Framework uses a variant of the Structured Query Language, named Entity SQL, which is aimed at writing declarative queries and updates over entities and entity relationships – at the conceptual level. It differs from SQL in that it does not have explicit constructs for joins because the EDM is designed to abstract partitioning data across tables.[citation needed]

Querying against the conceptual model is facilitated by EntityClient classes, which accepts an Entity SQL query. The query pipeline parses the Entity SQL query into a command tree, segregating the query across multiple tables, which is handed over to the EntityClient provider. Like ADO.NET data providers, an EntityClient provider is also initialized using a Connection object, which in addition to the usual parameters of data store and authentication info, requires the SDL schema and the mapping information. The EntityClient provider in turn then turns the Entity SQL command tree into an SQL query in the native flavor of the database. The execution of the query then returns an Entity SQL ResultSet, which is not limited to a tabular structure, unlike ADO.NET ResultSets.[citation needed]

Entity SQL enhances SQL by adding intrinsic support for:[citation needed]

Entity SQL canonical functions[]

Canonical functions are supported by all Entity Framework compliant data providers. They can be used in an Entity SQL query. Also, most of the extension methods in LINQ to Entities are translated to canonical functions. They are independent of any specific database. When ADO.NET data provider receives a function, it translates it to the desired SQL statement.[32]

But not all DBMSs have equivalent functionality and a set of standard embedded functions. There are also differences in the accuracy of calculations. Therefore, not all canonical functions are supported for all databases, and not all canonical functions return the same results.[citation needed]

Group Canonical functions[32]
Aggregate functions Avg, BigCount, Count, Max, Min, StDev, StDevP, Sum, Var, VarP
Math functions Abs, Ceiling, Floor, Power, Round, Truncate
String functions Concat, Contains, EndsWith, IndexOf, Left, Length, LTrim, Replace, Reverse, Right, RTrim, Substring, StartsWith, ToLower, ToUpper, Trim
Date and Time functions AddMicroseconds, AddMilliseconds, AddSeconds, AddMinutes, AddHours, AddNanoseconds, AddDays, AddYears, CreateDateTime, AddMonths, CreateDateTimeOffset, CreateTime, CurrentDateTime, CurrentDateTimeOffset, CurrentUtcDateTime, Day, DayOfYear, DiffNanoseconds, DiffMilliseconds, DiffMicroseconds, DiffSeconds, DiffMinutes, DiffHours, DiffDays, DiffMonths, DiffYears, GetTotalOffsetMinutes, Hour, Millisecond, Minute, Month, Second, TruncateTime, Year
Bitwise functions BitWiseAnd, BitWiseNot, BitWiseOr, BitWiseXor
Other functions NewGuid

LINQ to Entities[]

The LINQ to Entities provider allows LINQ to be used to query various RDBMS data sources. Several database server specific providers with Entity Framework support are available.[citation needed]

Native SQL[]

In the Entity Framework v4 new methods ExecuteStoreQuery() and ExecuteStoreCommand() were added to the class ObjectContext.[citation needed]

Visualizers[]

Visual Studio has a feature called Visualizer. A LINQ query written in Visual Studio can be viewed as Native SQL using a Visualizer during debug session. A Visualizer for LINQ to Entities (Object Query) targeting all RDBMS is available in the "VisualStudioGallery".[33]

Entity Framework Profiler[]

The Entity Framework Profiler is an Object–Relational Mapping tool (ORM) that will troubleshoot performance issues in an ASP.NET application using Entity Framework. It scans for common database query inefficiencies like the SELECT N + 1 issue.[34]

See also[]

References[]

  1. ^ "Releases · dotnet/ef6 · GitHub".
  2. ^ "Releases · dotnet/efcore · GitHub".
  3. ^ Krill, Paul (20 July 2012). "Microsoft open-sources Entity Framework". InfoWorld. Retrieved 2012-07-24.
  4. ^ "Entity Framework Overview - ADO.NET".
  5. ^ ADO .NET Entity Framework Vote of No Confidence
  6. ^ "Update on the Entity Framework in .NET 4 and Visual Studio 2010". ADO.NET team blog. May 11, 2009. Archived from the original on January 20, 2010. Retrieved November 1, 2011.
  7. ^ "EF4.3.1 and EF5 Beta 1 Available on NuGet". ADO.NET team blog. February 29, 2012. Archived from the original on March 25, 2012. Retrieved March 27, 2012.
  8. ^ "EF5 Available on CodePlex". August 11, 2012.
  9. ^ "EF6 RTM Available". October 17, 2013. Archived from the original on 2014-03-30.
  10. ^ "Entity Framework - Home". September 14, 2016.
  11. ^ "EF Version History".
  12. ^ a b "EF7 - New Platforms, New Data Stores". May 19, 2014. Archived from the original on 2015-09-29.
  13. ^ "Entity Framework Core 1.0.0 Available". 27 June 2016.
  14. ^ Hanselman, Scott. "ASP.NET 5 is dead - Introducing ASP.NET Core 1.0 and .NET Core 1.0 - Scott Hanselman". www.hanselman.com. Retrieved 2016-07-11.
  15. ^ "Announcing .NET Core 2.0". .NET Blog. 14 August 2017.
  16. ^ "Announcing .NET Core 3.0". .NET Blog. 23 September 2019.
  17. ^ "EF Core releases and planning".
  18. ^ "Microsoft.EntityFrameworkCore 5.0.11".
  19. ^ "EF Core releases and planning".
  20. ^ "Microsoft.EntityFrameworkCore 5.0.11".
  21. ^ "EF Core releases and planning".
  22. ^ "Microsoft.EntityFrameworkCore 6.0".
  23. ^ "Entity Data Model". MSDN, Microsoft. August 2, 2012. Retrieved August 15, 2013.
  24. ^ CSDL, SSDL, and MSL Specifications, MSDN, archived from the original on 2010-11-08, retrieved 2010-12-06
  25. ^ Entity Data Model Wizard, MSDN, retrieved 2010-12-06
  26. ^ Kogent Solutions Inc. (2009), ASP.NET 3.5 Black Book, Dreamtech Press, ISBN 978-81-7722-831-1
  27. ^ a b Simple Types (EDM), MSDN, retrieved 2010-12-06
  28. ^ ComplexType Element (CSDL), MSDN, retrieved 2010-12-06
  29. ^ Conceptual Model Types, MSDN, retrieved 2010-12-06
  30. ^ OnDelete Element (CSDL), MSDN, retrieved 2010-12-06
  31. ^ Facets (CSDL), MSDN, retrieved 2010-12-06
  32. ^ a b Canonical Functions (Entity SQL), MSDN, retrieved 2010-03-29
  33. ^ VisualStudioGallery
  34. ^ "Entity Framework Profiler". hibernatingrhinos.com. Hibernating Rhinos. Retrieved 2021-05-12.

Bibliography[]

External links[]