OR Impedance OR Impedance MismatchMismatch

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OR Impedance OR Impedance MismatchMismatch•Conflicting type systemsConflicting type systems•Conflicting design goalsConflicting design goals

Database system focuses specifically on the storage and retrieval of data, whereas an object Database system focuses specifically on the storage and retrieval of data, whereas an object system focuses specifically on the union of state and behavior for easier programmer system focuses specifically on the union of state and behavior for easier programmer manipulationmanipulation

•Conflicting architectural styleConflicting architectural styleMost database products are built to assume a fundamentally client/server style of interaction, Most database products are built to assume a fundamentally client/server style of interaction, assuming the database is located elsewhere on the network, and programs accessing the assuming the database is located elsewhere on the network, and programs accessing the database will be doing so via some sort of remote access protocol. Object systems assume the database will be doing so via some sort of remote access protocol. Object systems assume the precise opposite, and in fact, perform significantly worse when distributed.precise opposite, and in fact, perform significantly worse when distributed.

•Differing structural relationshipsDiffering structural relationshipsRelational data stores track entities in terms of relations between tuples and tuplesets; object-Relational data stores track entities in terms of relations between tuples and tuplesets; object-oriented systems instead prefer to track entities in terms of classes, compilation of state and oriented systems instead prefer to track entities in terms of classes, compilation of state and behavior that relates to one another through IS-A and/or HAS-A style unidirectional behavior that relates to one another through IS-A and/or HAS-A style unidirectional connections. Where databases use foreign-key relationships to indicate relations, objects use connections. Where databases use foreign-key relationships to indicate relations, objects use references or pointersreferences or pointers

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OR Impedance OR Impedance MismatchMismatch•Differing identity constructsDiffering identity constructs

Object systems use an implicit sense of identity to distinguish between objects of similar state Object systems use an implicit sense of identity to distinguish between objects of similar state (the ubiquitous this pointer or reference), yet databases require that sense of identity to be (the ubiquitous this pointer or reference), yet databases require that sense of identity to be explicit via primary key column or columns. In fact, in modern object-oriented languages an explicit via primary key column or columns. In fact, in modern object-oriented languages an object system cannot be built without a sense of object identity, whereas relational tables can object system cannot be built without a sense of object identity, whereas relational tables can have no primary key whatsoever, if desired.have no primary key whatsoever, if desired.

•Transactional boundariesTransactional boundariesObject systems do not have any sense of "transactional demarcation" when working with the Object systems do not have any sense of "transactional demarcation" when working with the objects, whereas database instances must in order to deal with the multi-user requirements of objects, whereas database instances must in order to deal with the multi-user requirements of

a modern client/server-based systema modern client/server-based system..•Query/access capabilitiesQuery/access capabilities

Retrieving data stored in a relational database makes use of SQL, a declarative language Retrieving data stored in a relational database makes use of SQL, a declarative language predicated on the mathematical theory of relational algebra and predicate. In object systems, predicated on the mathematical theory of relational algebra and predicate. In object systems, the entire object is required in order to navigate from one object to the next, meaning that the the entire object is required in order to navigate from one object to the next, meaning that the entire graph of objects is necessary in order to find two disparate parts of data—for a system entire graph of objects is necessary in order to find two disparate parts of data—for a system intended to remain entirely in working memory, this is of no concern, but for a system whose intended to remain entirely in working memory, this is of no concern, but for a system whose principal access is intended to be distributed, as relational database are, this can be a principal access is intended to be distributed, as relational database are, this can be a crippling problem.crippling problem.

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Object Relational Object Relational MappingMappingWikipedia defines an ORM as: “a programming defines an ORM as: “a programming

technique for converting data between incompatible technique for converting data between incompatible type systems in relational databases and object-type systems in relational databases and object-oriented programming languages. This creates, in oriented programming languages. This creates, in effect, a "virtual object database," which can be used effect, a "virtual object database," which can be used from within the programming language.” An ORM from within the programming language.” An ORM has to provide a facility to map database tables to has to provide a facility to map database tables to domain objects, using a design surface or wizard. domain objects, using a design surface or wizard. This mapping is in-between your database and This mapping is in-between your database and domain model, independent from the source code domain model, independent from the source code and the database. The ORM runtime then converts and the database. The ORM runtime then converts the commands issued by the domain model against the commands issued by the domain model against the mapping into back end database retrieval and the mapping into back end database retrieval and SQL statements. Mapping allows an application to SQL statements. Mapping allows an application to deal seamlessly with several different database deal seamlessly with several different database models, or even databases.models, or even databases.

The LINQ ProjectThe LINQ Project

StandardStandardQueryQuery

OperatorsOperators

ObjectsObjects

DLinqDLinq(ADO.NET)(ADO.NET)

XLinqXLinq(System.Xml)(System.Xml)

<book><book> <title/><title/> <author/><author/> <year/><year/> <price/><price/></book></book>

XMLXML

.NET Language Integrated Query.NET Language Integrated Query

C#C# VBVB Others…Others…

SQLSQL WinFWinFSS

SqlConnection c = new SqlConnection c = new SqlConnection(…);SqlConnection(…); c.Open(); c.Open(); SqlCommand cmd = new SqlCommand(SqlCommand cmd = new SqlCommand( @"SELECT c.Name, c.Phone@"SELECT c.Name, c.Phone

FROM Customers cFROM Customers c WHERE c.City = @p0"WHERE c.City = @p0"

);); cmd.Parameters.AddWithValue("@po", cmd.Parameters.AddWithValue("@po", "London"); "London"); DataReader dr = c.Execute(cmd); DataReader dr = c.Execute(cmd); while (dr.Read()) {while (dr.Read()) { string name = dr.GetString(0);string name = dr.GetString(0); string phone = dr.GetString(1);string phone = dr.GetString(1); DateTime date = DateTime date = dr.GetDateTime(2);dr.GetDateTime(2); }} dr.Close();dr.Close();

Data Access In APIs TodayData Access In APIs Today

Queries in Queries in quotesquotes

Arguments Arguments loosely loosely boundbound

Results Results loosely loosely typedtypedCompiler Compiler cannot cannot

help catch help catch mistakesmistakes

Data Access with DLINQData Access with DLINQ

public class Customerpublic class Customer{{ public int Id;public int Id; public string Name;public string Name; public string Phone;public string Phone; … …}}

Table<Customer> customers = Table<Customer> customers = db.Customers;db.Customers;

var contacts =var contacts = from c in customersfrom c in customers where c.City == "London"where c.City == "London" select new { c.Name, c.Phone };select new { c.Name, c.Phone };

Classes Classes describe describe

datadataTables are Tables are collectionscollections

Query is Query is natural natural

part of the part of the languagelanguageThe The compiler compiler helps you helps you

outout

public class Customer { public class Customer { …… } }

public class Northwind: public class Northwind: DataContextDataContext

{{ public Table<Customer> public Table<Customer>

Customers;Customers; ……

}}

Northwind db = new Northwind(Northwind db = new Northwind(……););var contacts =var contacts =

from c in db.Customersfrom c in db.Customers where c.City == "London"where c.City == "London"

select new { c.Name, c.Phone };select new { c.Name, c.Phone };

DLinq For Relational DataDLinq For Relational Data

AccessingAccessing data with DLinqdata with DLinqClasses Classes

describe datadescribe data

Strongly typed Strongly typed connectionconnection

Integrated Integrated query syntaxquery syntax

Strongly typed Strongly typed resultsresults

Tables are Tables are like collectionslike collections

ArchitectureArchitecture

LINQ QueryLINQ Query ObjectsObjects SubmitChangeSubmitChanges()s()

SQL QuerySQL Query RowsRows SQL or SQL or Stored Stored ProcsProcs

DLinqDLinq(ADO.NET)(ADO.NET)

SQLSerSQLServerver

from c in db.Customersfrom c in db.Customerswhere c.City == "London"where c.City == "London"selectselect new { c.Name, c.Phone } new { c.Name, c.Phone }

select Name, Phoneselect Name, Phonefrom customersfrom customerswhere city = 'London'where city = 'London'

ApplicationApplication

Services:Services:- Change tracking- Change tracking- Concurrency control- Concurrency control- Object identity- Object identity

Key TakeawaysKey Takeaways

Language integrated data accessLanguage integrated data access

Maps tables and rows to classes and objectsMaps tables and rows to classes and objects

Builds on ADO.NET and .NET TransactionsBuilds on ADO.NET and .NET Transactions

MappingMapping

Encoded in attributesEncoded in attributes

Relationships map to propertiesRelationships map to properties

Manually authored or tool generatedManually authored or tool generated

PersistencePersistence

Automatic change trackingAutomatic change tracking

Updates through SQL or stored proceduresUpdates through SQL or stored procedures

DataContextDataContext

Strongly typed databaseStrongly typed database

Querying For ObjectsQuerying For Objects

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Key TakeawaysKey Takeaways

Language Integrated QueryLanguage Integrated QueryCompile-time type checking, IntelliSenseCompile-time type checking, IntelliSense

SQL-like query syntaxSQL-like query syntaxWith support for hierarchy and With support for hierarchy and relationshipsrelationships

Intelligent object loadingIntelligent object loadingDeferred or immediateDeferred or immediate

Updating ObjectsUpdating Objects

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Key TakeawaysKey Takeaways

Auto-generated updatesAuto-generated updatesUsing optimistic concurrencyUsing optimistic concurrency

TransactionsTransactionsIntegrates with System.TransactionsIntegrates with System.Transactions

SQL pass-throughSQL pass-throughReturning objects from SQL queriesReturning objects from SQL queries

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DLinq SummaryDLinq Summary

Allows access to relational data as Allows access to relational data as objectsobjects

Supports Language Integrated QuerySupports Language Integrated Query

Works with existing infrastructureWorks with existing infrastructure

Unifies programming model for Unifies programming model for objects, relational and XMLobjects, relational and XML

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When to Use LINQ to When to Use LINQ to SQL?SQL?The primary scenario for using LINQ to SQL is when The primary scenario for using LINQ to SQL is when

building applications with a rapid development cycle building applications with a rapid development cycle and a simple one-to-one object to relational mapping and a simple one-to-one object to relational mapping against the Microsoft SQL Server family of databases. against the Microsoft SQL Server family of databases. In other words, when building an application whose In other words, when building an application whose object model is structured very similarly to the object model is structured very similarly to the existing database structure, or when a database for existing database structure, or when a database for the application does not yet exist and there is no the application does not yet exist and there is no predisposition against creating a database schema predisposition against creating a database schema that mirrors the object modelthat mirrors the object model

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When to Use LINQ to When to Use LINQ to SQL?SQL?

I want to… LINQ to SQL is applicable

Use an ORM solution and my database is 1:1 with my object model

Use an ORM solution with inheritance hierarchies that are stored in a single table

Use my own plain CLR classes instead of using generated classes or deriving from a base class or implementing an interface

Leverage LINQ as the way I write queries

Use an ORM but I want something that is very performant and where I can optimize performance through stored procedures and compiled queries