Entity Framework

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Entity Framework

Bibliografie

Site Microsoft

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EF - Prerequisites

 Cunostinte despre .NET Framework, C#, MS SQL Server, Visual Studio.

 ADO .NET Architecture.

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EF - Tools

– Visual Studio 2017 sau 2019.

– SQL Server … sau SQLExpress Edition.

– Entity Framework actualizat folosind NuGet

Package.

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Entity Framework

• Entity Framework 6

• Entity Framework Core

• EF 6 vs EF Core

Managed Provider DataReader Command

Connection

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Managed Provider DataReader Command

Connection

ADO.NET Architecture

Controls, Designers, Code-gen, etc

DataSet

DataAdapter XmlReader

XmlWriter

OLTP operations,

Programmatic Processing,

Frameworks

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ADO.NET Data Provider

• Specific pentru fiecare DBMS

– Expune in mod direct interfete catre consumatori.

• ADO.NET DataProvider Object Model

– Connection

• Stabileste o conexiune la DataSource

– Transaction

• Control explicit al tranzactiei

– Command

• Executa instructiuni SQL

– DataReader

• Forward-only, Read-Only

Data store

Data Provider

Connection

CreateCommand()

ExecuteReader() DataReader

Command Parameters Parameters Parameters

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Ce este EF?

• EF este un “Object Relational Mapping (ORM) framework” ce ofera dezvoltatorilor un

mecanism automat pentru memorarea si

accesarea datelor intr-o baza de date.

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Continuare

• EF apare in 2008. Scop principal: interactiunea

dintre aplicatiile .NET si baze de date relationale.

• Roluri ORM:

– Creaza conexiunea la baza de date.

– Executa comenzi asupra bazei de date.

– Transforma rezultatele cererilor ca obiecte ale aplicatiei.

– Gestioneaza modificarile efectuate asupra obiectelor aplicatiei.

– Memoreaza aceste modificari in baza de date.

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De ce Entity Framework?

• Scopul unui ORM este de a creste productivitatea prin reducerea task-urilor redundante in ceea ce priveste persistenta datelor folosite in aplicatii.

• EF poate genera si executa comenzile necesare pentru citirea/scrierea datelor in baza de date.

• Se pot efectua cereri asupra obiectelor din model folosind “LINQ to Entities”.

• Rezultatul cererilor in EF este materializat in

obiecte si nu in scalari ca in ADO.NET.

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// ADO .NET

SqlConnection connection =

new SqlConnection(connectionString);

connection.Open();

String query = “Select id, Titlu From Curs”;

SqlCommand command = new SqlCommand(query, connection);

SqlDataReader reader = command.ExecuteReader();

while(reader.Read()) {

int id = reader.GetInt32(0);

string titlu = reader.GetString(1);

// … }

reader.Close();

command.Dispose(); // command.Close(); !!!

connection.Close();

Exemplu utilizare Connection, Command si DataReader

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Putem lucra la acest nivel

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Exemplu: EntityConnection, EntityCommand, ExecuteReader

// Specify the provider name, server and database.

string providerName = "System.Data.SqlClient";

string serverName = ".";

string databaseName = "AdventureWorks";

SqlConnectionStringBuilder sqlBuilder = new

SqlConnectionStringBuilder();

sqlBuilder.DataSource = serverName;

sqlBuilder.InitialCatalog = databaseName;

sqlBuilder.IntegratedSecurity = true;

string providerString = sqlBuilder.ToString();

EntityConnectionStringBuilder entityBuilder =

new EntityConnectionStringBuilder();

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Continuare

//Set the provider name.

entityBuilder.Provider = providerName;

// Set the provider-specific connection string.

entityBuilder.ProviderConnectionString = providerString;

// Set the Metadata location. New!!!

entityBuilder.Metadata =

@"res://*/AdventureWorksModel.csdl|

res://*/AdventureWorksModel.ssdl|

res://*/AdventureWorksModel.msl";

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Continuare

using (EntityConnection conn =

new EntityConnection(entityBuilder.ToString())) {

conn.Open();

EntityCommand cmd = new EntityCommand(query, conn);

using (EntityDataReader reader = cmd.ExecuteReader()) {

while (reader.Read()) {

// … }

conn.Close();

}

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De ce Entity Framework?

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De ce Entity Framework?

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EF - modele

• Model Conceptual.

• Model memorare.

• Model mapare.

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EF – model conceptual

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Continuare

• Cererile se executa direct asupra obiectelor din modelul conceptual.

• Se foloseste o singura metoda –

SaveChanges() - pentru a salva datele in baza

de date.

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Trasaturi

• Entity Framework este un tool Microsoft.

• EF exista in doua versiuni: V6 si EF Core

• EF Core este dezvoltat ca un produs Open Source.

• EF lucreaza cu bd ce au un furnizor de EF.

• EF genereaza comenzi SQL din LINQ to Entities.

• EF creaza cereri parametrizate.

• EF gestioneaza evidenta modificarilor obiectelor din memorie (obiecte din model).

• EF permite generarea comenzilor insert, update si delete.

• EF are suport pentru proceduri catalogate.

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Entity Framework - Architecture

• EF – Data Provider.

• EF – Entity Client.

• EF - Object Service.

Aceste niveluri au fost evidentiate pe un slide anterior.

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Continuare - Data Provider

• Data Provider

– Specific fiecarui furnizor de baze de date, ce abstractizeaza interfetele ADO.NET pentru

conectare la baza de date cand lucram cu schema conceptuala.

– Translateaza LINQ to entities la expresii SQL valide

si le executa asupra bazei de date.

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Continuare – Entity Client

• Entity Client

– Model Conceptual – Model Mapare

– Model Memorare

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Continuare – Object Service

• Object Service

– Object Context, reprezinta sesiunea interactiunii intre aplicatii si sursa de date.

– Object Context - executa diverse operatii asupra entitatilor (add, delete, update, save).

– Gestioneaza starea modificarilor entitatilor (Track Changes).

– Gestioneaza rezultatele cererilor.

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EF 6

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Exemplu

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Modelul

public partial class Post {

public Post() { this.Comments = new HashSet<Comment>(); } [DataMember]

public int PostId { get; set; } [DataMember]

public string Description { get; set; } [DataMember]

public string Domain { get; set; } [DataMember]

public System.DateTime Date { get; set; } [DataMember]

public virtual ICollection<Comment> Comments { get; set; } }

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Continuare

public partial class Comment {

[DataMember]

public int CommentId { get; set; } [DataMember]

public string Text { get; set; } [DataMember]

public int PostPostId { get; set; }

[DataMember]

public virtual Post Post { get; set; } }

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Continuare - Contextul

public partial class ModelPostCommentContainer : DbContext {

public ModelPostCommentContainer() :

base("name=ModelPostCommentContainer") { Configuration.LazyLoadingEnabled = false;

Configuration.ProxyCreationEnabled = false;

}

protected override void OnModelCreating(

DbModelBuilder modelBuilder) { throw new UnintentionalCodeFirstException(); }

public virtual DbSet<Post> Posts { get; set; }

public virtual DbSet<Comment> Comments { get; set; } }

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CSDL generat

• VS 2019 deschide solutie din

D:\Documente\Cursuri\Curs special NET\WCF\Code\PostComment

• Se vor vizualiza csdl, msl, ssdl

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Continuare

• Structura tabele

CREATE TABLE [dbo].[Posts] (

[PostId] INT IDENTITY (1, 1) NOT NULL, [Description] NVARCHAR (MAX) NOT NULL, [Domain] NVARCHAR (MAX) NOT NULL, [Date] DATETIME NOT NULL,

CONSTRAINT [PK_Posts] PRIMARY KEY CLUSTERED ([PostId] ASC)

);

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Continuare

CREATE TABLE [dbo].[Comments] (

[CommentId] INT IDENTITY (1, 1) NOT NULL, [Text] NVARCHAR (MAX) NOT NULL, [PostPostId] INT NOT NULL,

CONSTRAINT [PK_Comments] PRIMARY KEY CLUSTERED ([CommentId] ASC),

CONSTRAINT [FK_CommentPost] FOREIGN KEY

([PostPostId]) REFERENCES [dbo].[Posts] ([PostId])

);

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Rezumat

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Exemple cod

• In solutia deschisa se vor exemplifica cateva

metode.

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ObjectContext

• Context object reprezinta accesul la serviciile din EF.

• Expune obiecte entitate.

• Gestioneaza conexiunile la baza de date.

• Genereaza SQL parametrizat.

• Transfera date in / din baza de date.

• Realizeaza cache la obiecte.

• Jurnalizeaza modificarile efectuate.

• Materializeaza sau transforma o multime rezultat fara

tip intr-o colectie de obiecte puternic tipizate.

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ObjectContext - metode

• AcceptAllChanges

• AddObject

• CreateDatabase

• DeleteDatabase

• DeleteObject

• DetectChanges

• ExecuteStoreCommand

• SaveChanges(SaveOptions)

• Attach

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ObjectSet - Metode

• AddObject

• ApplyCurrentValues

• Attach

• DeleteObject

• Detach

• Execute

• Include

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DbContext

• Conceptual aceasta clasa este similara cu

ObjectContext. Se foloseste pentru a executa cereri asupra EDM si a efectua actualizarea bazei de date (insert, update, delete, cereri). Aceasta clasa este folosita in versiunile EF mai mari sau egale cu 4.1.

public class ProductContext : DbContext { // cod lipsa ...

public DbSet<Post> Posts { get; set; }

public DbSet<Comment> Comments { get; set; }

}

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DbContext - Continuare

• Accesarea unei proprietati DbSet din cadrul contextului reprezinta definitia unei cereri ce returneaza (toate)

entitatile de tipul specificat. Faptul ca accesam o

proprietate nu inseamna ca cererea se executa. O cerere este executata cand:

• Este enumerata in foreach.

• Este enumerata de o operatiune din colectie cum ar fi ToArray, ToDictionary sau ToList.

• Sunt specificati in cadrul cererii operatorii LINQ First sau Any .

• Sunt apelate urmatoarele metode: metoda extinsa Load pe un DbSet, DbEntityEntry.Reload si

Database.ExecuteSqlCommand.

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Proprietati pentru DbContext

• ChangeTracker

• Configuration

• Database

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DbContext - Metode

• Entry(Object); Entry<TEntity> (TEntity)

• Gets a DbEntityEntry object for the given entity providing access to information about the entity and the ability to perform actions on the entity.

• OnModelCreating()

• This method is called when the model for a derived context has been initialized, but before the model has been locked down and used to initialize the context.

• SaveChanges(); SaveChangesAsync(); SaveChangesAsync(

CancellationToken)

• Set(Type); Set<TEntity>()

• Returns a DbSet instance for access to entities of the given type in the context, the ObjectStateManager, and the underlying store.

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Proprietatea Database

• Prin proprietatea Database obtinem un obiect Database. Acest obiect expune metode ce pot executa comenzi SQL (DDL/DML) la nivel de baza de date.

• Clasa Database expune proprietatea

Connection ce permite recrearea unui obiect

DbConnection daca acesta nu exista.

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DbSet, DbSet<Tentity>

• Add ; AddRange

• Attach

• Find

• Include - Specifies the related objects to include in the query results. (Inherited from DbQuery<TResult>.)

• Remove ; RemoveRange

• SqlQuery

• Creates a raw SQL query that will return entities in this set. By

default, the entities returned are tracked by the context; this can be changed by calling AsNoTracking on

the DbSqlQuery<TEntity> returned. Note that the entities returned are always of the type for this set and never of a derived type. If the table or tables queried may contain data for other entity types,

then the SQL query must be written appropriately to ensure that only entities of the correct type are returned.

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Cereri pe Entity Data Model - EDM

• EF foloseste informatiile din model si fisierele de mapare pentru a translata cererile asupra obiectelor din modelul conceptual in cereri specifice sursei de date.

• EF furnizeaza urmatoarele modalitati de a interoga modelul conceptual si a returna obiecte:

o LINQ to Entities. Furnizeaza suport pentru Language-Integrated Query (LINQ) in vederea interogarii tipurilor de entitati definite in modelul conceptual.

o Entity SQL. Un dialect SQL independent de mediul de memorare ce lucreaza direct cu entitatile in modelul conceptual.

o Metode de constructie a cererilor folosind metodele din LINQ to Objects.

o SQL nativ.

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Incarcare date relationate

• La ce se refera?

• Proprietati de navigare:

– Tip referinta (Reference).

– Tip colectie (Collection).

• Lazy loading

• Eager loading

• Explicit loading

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Lazy loading

• Implicit. Cerintele pe care trebuie sa le

indeplineasca clasele POCO definite sunt:

• Sa fie public dar nu sealed.

• Proprietatile de navigare - virtual.

• DbContext.Configuration.LazyLoadingEnable d. Implicit este setata pe true.

• Proxy dinamic creat intern.

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Eager loading

• Include :

• var query =

context.Posts.Include(“Comments").Take(5);

• var query = from item in

context.Posts.Include(ct=>ct.Comments) where ct.Text == “gRPC”

select ct;

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Explicit loading

• Entry()- stabilire intrare pentru entitatea data.

• Collection();

• Reference();

• Property(); CurrentValue;

• Load();

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Exemplu - Collection

//Disable Lazy loading

ctx.Configuration.LazyLoadingEnabled = false;

var itemsPost= from post in ctx.Posts where post.PostId == 1

select post;

var single = itemsPost.Single();

ctx.Entry(single)

.Collection(d => d.Comments)

.Load();

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Exemplu - Reference

//Disable Lazy loading

ctx.Configuration.LazyLoadingEnabled = false;

var itemsCom= from com in ctx.Comments where post.CommentId == 10

select com;

var single = itemsCom.Single();

ctx.Entry(single)

.Reference(d => d.Posts)

.Load();

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Property – doua prototipuri

using (var context = new BloggingContext()) {

var blog = context.Blogs.Find(3);

// Read the current value of the Name property string currentName1 = context.Entry(blog)

.Property(u => u.Name).CurrentValue;

// Set the Name property to a new value

context.Entry(name).Property(u => u.Name).CurrentValue = "My Fancy Blog";

// Read the current value of the Name property //using a string for the property name

object currentName2 = context.Entry(blog).Property("Name").CurrentValue;

// Set the Name property to a new value using // a string for the property name

context.Entry(blog).Property("Name").CurrentValue = "My Boring Blog";

}

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Explicit loading - continuare

• IsModified – proprietate scalara.

• IsLoaded – continut proprietate de navigare

incarcat sau nu.

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Entity Framework si aplicatii N-tier

• Jurnalizare:

– Snapshot change tracking (fara notificare context).

• DetectChanges() din ChangeTracker.

– Change tracking proxies (cu notificare context).

Clasele sa fie publice si sa nu fie sealed.

Proprietatile sa fie virtuale. Getter-i si setter-i sa fie publici.

Proprietatile de navigare de tip colectie sa fie de tipul

ICollection<T>.

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Exemplu

public partial class CustomerType {

public CustomerType() {

this.Customers = new HashSet<Customer>();

}

// Proprietati scalare

public virtual int CustomerTypeId { get; set; } public virtual string Description { get; set; } // Entitate colectie

public virtual ICollection<Customer> Customers { get; set; } }

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Detectie modifificari

• Metode implicate:

• DbSet.Add

• DbSet.Find

• DbSet.Remove

• DbSet.Local

• DbContext.SaveChanges

• Rulare cerere LINQ asupra unui DbSet

• DbSet.Attach

• DbContext.GetValidationErrors

• DbContext.Entry

• DbChangeTracker.Entries

• Detectarea modificarilor poate fi setata pe on sau off astfel:

context.Configuration.AutoDetectChangesEnabled = false; // true = on

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DetectChanges() si …

• Metoda DetectChanges() este responsabila si pentru a sincroniza relatiile existente intre

entitati, entity reference sau entity collection.

Acest lucru este vizibil atunci cand folosim data binding in aplicatii GUI si facem

modificari asupra proprietatilor de navigare.

Modificarile efectuate trebuie sa se reflecte in interfata GUI a aplicatiei.

• AsNoTracking() ???

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DbContext - State

Proprietatea State.

Enumerarea EntityState

{

Unchanged, Added,

Modified,

Deleted,

Detached

}

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EntityState

context.Entry(item).State = EntityState.Added;

context.SaveChanges();

context.Entry(item).State = EntityState.Unchanged;

context.Entry(item).State = EntityState.Modified;

context.Entry(item).State = EntityState.Deleted;

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Scenariu cu entitati deconectate

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EF Core

• Configurare – OnConfiguring()

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)

• Creare model – OnModelCreating()

protected override void OnModelCreating(ModelBuilder modelBuilder)

• Salvare date – SaveChanges()

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EF Core Fluent API

Entity Framework Core Fluent API configures the following aspects of a model:

• Model Configuration: Configures an EF model to database mappings. Configures the default Schema, DB functions, additional data annotation attributes and entities to be excluded from mapping.

• Entity Configuration: Configures entity to table and

relationships mapping e.g. PrimaryKey, AlternateKey, Index, table name, one-to-one, one-to-many, many-to-many

relationships etc.

• Property Configuration: Configures property to column

mapping e.g. column name, default value, nullability,

Foreignkey, data type, concurrency column etc.

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Model configurations

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Entity configuration

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Property configuration

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Exemplu (1 -> *)

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Exemplu (1 -> 1)

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DbContext - DbSet

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Working with Disconnected Entity Graph in Entity Framework Core

• Attach()

• Entry()

• Add()

• Update()

• Remove()

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Attach()

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Entry()

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Add()

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Update()

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Remove()

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ChangeTracker.TrackGraph() in Entity Framework Core

Purpose: To track the entire entity graph and set custom entity states to each entity in a graph.

The ChangeTracker.TrackGraph() method begins tracking an entity and any entities that are reachable by traversing it's

navigation properties. The specified callback is called for each

discovered entity and an appropriate EntityState must be set

for each entity. The callback function allows us to implement a

custom logic to set the appropriate state. If no state is set, the

entity remains untracked.

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Execute Raw SQL Queries in Entity Framework Core

• Metode redenumite: FromSql, ExecuteSql, ExecuteSqlAsync in

– FromSqlRaw,

– ExecuteSqlRaw, si

– ExecuteSqlRawAsync.

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