1C# kursus Rohde & Schwarz

Object Relational Mapping – ORMEntity Framework

Entity Framework

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ORM?

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Objects vs. Relations

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Object-Relational Impedance Mismatch

Object-Oriented RelationalBased on proven software engineering principles.Entry point is behaviourObject collections and associations derived from graph theory

Based on proven mathematical principles.Entry point is dataData collections and associations derived from set theory

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A Physical Data Model

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A Class Model

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Differences

Physical Data Model Class Model

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Benefits Of O/R Mapping

Clean OO designHiding the relational model specifics lets the object model be more cleanly analyzed and applied.

ProductivitySimpler code as the object model is free from persistence constraints. Developers can navigate object hierarchies, etc.

Separation of concerns and specializationLet the DB people worry about DB structure and the Object people worry about their OO models.

Time savingsThe O/R mapping layer saves you from writing the code to persist and retrieve objects. O/R mapping tool vendors claim 20-30% reduction in the code that needs to be written. Writing less code also means less testing.

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Drawbacks Of O/R Mapping

Usually commit the "Needless Repetition" deadly sin (a.k.a. DRY – "Don't Repeat Yourself“)

The table structure as well as their relations are stored both in the DB and in the mapping files used by the O/R mapper

Writing mapping files is a huge taskNeeds to be updated every time the database layout is changed

QueriesLimited query capabilities…… or performance problems on complicated queries

Some O/R mappers implement caches, lazy initialization, batch modes etc. to help avoid the performance problems

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ENTITY FRAMEWORK

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Entity Framework

What is Entity Framework?Entity Framework (EF) is an object-relational mapper that enables .NET developers to work with relational data using domain-specific objects. It eliminates the need for most of the data-access code that developers usually need to write.

http://msdn.microsoft.com/en-us/data/ef.aspx

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Supported Databases

MS SQL ServerMySQLSQLiteOracleFirebirdPostgreSQL... and more

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Getting Started

EF supports four development workflows:http://msdn.microsoft.com/en-us/data/jj590134

Find out which fits your conditions:http://msdn.microsoft.com/en-us/data/ee712907

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Installation

Pre installed with Visual Studio 2012Can be installed with NuGet in Visual Studio 2010

You might need to install NuGet first...

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Using Entity Framework

Create a mapping of your databaseEntity Data Model (Model First)

Database migrations not possible (yet)Plain Old CLR Objects (POCO) (Code First)

Database migrations possible

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Using Entity Framework

Connect through a sub class of DbContext

Make queries using LINQ

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Demo