How is the generated query created in Linq when we do UPDATE?

As the context ( DbContext ) works when I call an entity by First() , FirstOrDefault() , Find(value) , ie I bring a record to change:

Model:

[Table("Credit")]
public class Credit
{
    public Credit()
    {
    }
    public Credit(string description)
    {
        Description = description;
    }
    public Credit(int id, string description)
    {
        Id = id;
        Description = description;
    }

    [Key()]  
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]        
    public int Id { get; set; }

    [Required()]
    [MaxLength(50)]
    public string Description { get; set; }

    public bool Status { get; set; }
    public int Lines { get; set; }
}

Context (DbContext):

public class Database  : DbContext
{
    public Database()
        :base(@"Server=.\SqlExpress;Database=dbtest;User Id=sa;Password=senha;")
    {
       Database.Initialize(false);
    }

    public DbSet<Credit> Credit { get; set; }    
}

Running operations:

class Program
{
    static void Main(string[] args)
    {
        using (Database db = new Database())
        {
            db.Database.Log = ca => WriteLog(ca);

            int value = 1;
            Credit cr = db.Credit.Find(value);
            cr.Lines = cr.Lines + 1;
            db.SaveChanges();

        }



        System.Console.WriteLine("Pression <Enter> ...");
    }

    public static void WriteLog(string c)
    {
        System.Console.WriteLine(c);
    }
}

In the code above, basic auditing is used, which shows which SQL is being generated, in the example case two are Select and Update , being an update only of what was modified, as shown in debug logo below:

Then,concludethattheupdateismadeonlyofthepropertythathasbeenchanged.

  

1-DoesContexthavesomewaytogeneratethesamesyntax?

Yesitgeneratesthesamesyntax,makingupdatesonlyofpropertiesthathavebeenchanged.

  

2-Isthereanywaytoseethequerybeingsenttothebankinthiscase?

Yes,itdoes,db.Database.LogwillbringtheSQLgeneratedbythecontext.

using(Databasedb=newDatabase()){db.Database.Log=ca=>WriteLog(ca);

CanalsobeusedintheDebugTracewindow:

db.Database.Log=ca=>System.Diagnostics.Debug.WriteLine(ca);

  

3-HowisContextmadeawarethatonlytheNamecolumnhaschanged?

Creditcr=db.Credit.Find(value);cr.Lines=cr.Lines+1;db.Entry(cr).Property(x=>x.Lines).IsModified

Thisshowsdb.Entry(cr).Property(x=>x.Lines).IsModifiedifthepropertyhaschanged,theContextisbasedonthetrueresponse(true),andthecodeonlychangeswhatismodifiedastrue.

Thereisnothingimplementedtocheckwhichfieldsaremodifiedatonce,butcanbeeasilydonebyanextensionmethod,totellwhichfieldshavechangedandwhichhavenot.

publicstaticclassMethodsUpdate{publicstaticDictionary<string,bool>GetUpdatePropertyNames<T>(thisDbEntityEntry<T>entry)whereT:class,new(){Dictionary<string,bool>entryUpdate=newDictionary<string,bool>();foreach(stringnameinentry.CurrentValues.PropertyNames){entryUpdate.Add(name,entry.Property(name).IsModified);}returnentryUpdate;}}Dictionary<string,bool>propertyChanges=db.Entry(cr).GetUpdatePropertyNames();

Inthisspecificcasethechangeinthebankhasnotyetbeenapplied,onlyinitscontext.

References:

• Entity Framework 6 - Generating SQL Command Log
• Logging and Intercepting Database Operations With Entity Framework 6.0
• Update only modified fields in Entity Framework
• How can I log the generated SQL from DbContext.SaveChanges () in my Program?
• Microsoft Developer Network - DbEntityEntry Class
• Entity Framework Tutorial - DBEntityEntry Class
• Get Table Name From DbEntityEntry (Code-First)
• Get Primary Key of DBEntityEntry when Adding
• Mocking or faking DbEntityEntry or creating a new DbEntityEntry

I do not know, but I do not think ... it makes sense to use entity when you want to do things with ADO.NET .

Yes. You can create your own logger or create a simple extension:

public static class QueryHelper
{
    public static string TraceSql<T>(this IQueryable<T> t)
    {
        var sql = "";
        ObjectQuery<T> oqt = t as ObjectQuery<T>;

        if (oqt != null)
            sql = oqt.ToTraceString();

        return sql;
    }
}

Or:

ctx.Database.Log = x => System.Diagnostics.Debug.WriteLine(x);

Through GetModifiedMembers or through a small implementation:

using (var ctx = new dbContext())
{
    var Produto = (from p in ctx.Produto
                            where p.Produto == 1
                            select p).FirstOrDefault();
    Produto.Nome = "Bombril";

    QueryHelper<Product>.Log(db, Produto);//seu logger

    ctx.SaveChanges();
}


public static class QueryHelper
{
    public static void Log<T>(DataContext dataContext, T entidade) where T : Class
    {
        foreach(var propriedadeModificada in dataContext.GetTable<T>().GetModifiedMembers(entidade))
        {
            var valorAtual = propriedadeModificada.CurrentValue;
            var valorOriginal = propriedadeModificada.OriginalValue;
        }
    }
}