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Reading a json file asynchronously, the object property results are always null

I have a Json file, it contains connectionstring. I want to asynchronously read the file and deserialize it to a ConnectionString object and I always get a null result. I'm using .NET Core 6 and System.Text.Json.
Here is contents of my Json file:
{
"ConnectionStrings": {
"ConnStr": "Data Source=(local);Initial Catalog=MyData;Integrated Security=False;TrustServerCertificate=True;Persist Security Info=False;Async=True;MultipleActiveResultSets=true;User ID=sa;Password=MySecret;",
"ProviderName": "SQLServer"
}
}
Here are the contents of my classes:
internal class DBConnectionString
{
[JsonPropertyName("ConnStr")]
public string ConnStr { get; set; }
[JsonPropertyName("ProviderName")]
public string ProviderName { get; set; }
public DBConnectionString()
{
}
}
public class DBConnStr {
private static string AppSettingFilePath => "appsettings.json";
public static async Task<string> GetConnectionStringAsync()
{
string connStr = "";
if (File.Exists((DBConnStr.AppSettingFilePath)))
{
using (FileStream sr = new FileStream(AppSettingFilePath, FileMode.Open, FileAccess.Read))
{
//string json = await sr.ReadToEndAsync();
System.Text.Json.JsonDocumentOptions docOpt = new System.Text.Json.JsonDocumentOptions() { AllowTrailingCommas = true };
using (var document = await System.Text.Json.JsonDocument.ParseAsync(sr, docOpt))
{
System.Text.Json.JsonSerializerOptions opt = new System.Text.Json.JsonSerializerOptions() { AllowTrailingCommas = true, PropertyNameCaseInsensitive = true };
System.Text.Json.JsonElement root = document.RootElement;
System.Text.Json.JsonElement element = root.GetProperty("ConnectionStrings");
sr.Position = 0;
var dbConStr = await System.Text.Json.JsonSerializer.DeserializeAsync<DBConnectionString>(sr, opt);
if (dbConStr != null)
{
connStr = dbConStr.ConnStr;
}
}
}
}
return connStr;
}
}
The following is the syntax that I use to call the GetConnectionStringAsync method:
string ConnectionString = DBConnStr.GetConnectionStringAsync().Result;
When the application is running in debug mode, I checked, on line
var dbConStr = await
System.Text.Json.JsonSerializer.DeserializeAsync(sr,
opt);
The DBConnectionString object property is always empty.
I also tried the reference on the Microsoft website, https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/how-to?pivots=dotnet-6-0 but it doesn't work succeed.
using System.Text.Json;
namespace DeserializeFromFileAsync
{
public class WeatherForecast
{
public DateTimeOffset Date { get; set; }
public int TemperatureCelsius { get; set; }
public string? Summary { get; set; }
}
public class Program
{
public static async Task Main()
{
string fileName = "WeatherForecast.json";
using FileStream openStream = File.OpenRead(fileName);
WeatherForecast? weatherForecast =
await JsonSerializer.DeserializeAsync<WeatherForecast>(openStream);
Console.WriteLine($"Date: {weatherForecast?.Date}");
Console.WriteLine($"TemperatureCelsius: {weatherForecast?.TemperatureCelsius}");
Console.WriteLine($"Summary: {weatherForecast?.Summary}");
}
}
}
Do you have a solution for my problem or a better solution? I appreciate all your help. Thanks
Sorry about my English if it's not good, because I'm not fluent in English and use google translate to translate it

To begin with, if you want to read information from appSettings.json, you should explore more into reading configurations. There are helper classes provided by .Net for the same.
Coming back to your code, if you want to use your own code for Json Deserialization, then you need to make the following change to it.
var dbConStr = System.Text.Json.JsonSerializer.Deserialize<DBConnectionString>(element.GetRawText(), opt);
where, element according to code shared in the question is defined as
System.Text.Json.JsonElement element = root.GetProperty("ConnectionStrings");
This ensures the Raw Json associated with the JsonElement ConnectStrings is de-serialized.
However, I recommend you to read more into Reading configurations using the IConfiguration and related .Net helpers.

C# EF, refresh context

I'm creating an app that should work with various sqlite databases (with same structure) and I want to be able to open and close different databases. I use EF6 and I just can't figure out how to open a different database file (and make EF to reload and use data from new file). There are many questions regarding this but none of them work for me.
this is my dbContext generated by EF
public partial class mainEntities : DbContext
{
public mainEntities()
: base("name=mainEntities")
{
}
...
}
this is how I use and try to update my context
class Db
{
private static mainEntities myDbInstance;
public static mainEntities MyDbInstance
{
get
{
if (myDbInstance == null)
{
myDbInstance = new mainEntities();
}
return myDbInstance;
}
}
public static void UpdateConnectionString(string pth)
{
StringBuilder sb = new StringBuilder();
sb.Append("metadata=res://*/Model1.csdl|res://*/Model1.ssdl|res://*/Model1.msl;");
sb.Append("provider=System.Data.SQLite.EF6;");
sb.Append("provider connection string=");
sb.Append("'");
sb.Append("datetime format=JulianDay;");
sb.Append("foreign keys=True;");
sb.Append("data source=");
sb.Append(pth);
sb.Append("'");
var config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
var connectionStringsSection = (ConnectionStringsSection)config.GetSection("connectionStrings");
connectionStringsSection.ConnectionStrings["mainEntities"].ConnectionString = sb.ToString();
connectionStringsSection.ConnectionStrings["mainEntities"].ProviderName = "System.Data.EntityClient";
config.Save();
ConfigurationManager.RefreshSection("connectionStrings");
Properties.Settings.Default.Save();
Properties.Settings.Default.Reload();
//reset context - does not work
MyDbInstance.Dispose();
myDbInstance = null;
}
}
I am able to update the connectionString,
var conn_str = System.Configuration.ConfigurationManager.ConnectionStrings["mainEntities"].ConnectionString;
returns correct string after I change database file, but data is loaded from the original one.
EDIT:
I check if the connection changed with simple WPF GUI
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
private void refresh_labels()
{
var conn_str = System.Configuration.ConfigurationManager.ConnectionStrings["mainEntities"].ConnectionString;
var rows_count =
(from d in Db.MyDbInstance.TagsFiles
select d).Count();
label1.Content = conn_str.Split(';')[4];
label2.Content = rows_count;
}
private void Button_Click(object sender, RoutedEventArgs e)
{
String DbFileName1 = #"c:\tmp\db1.db3";
String DbFileName2 = #"c:\tmp\db2.db3";
var conn_str = System.Configuration.ConfigurationManager.ConnectionStrings["mainEntities"].ConnectionString;
if (conn_str.Contains(DbFileName1))
{
Db.UpdateConnectionString(DbFileName2);
}
else
{
Db.UpdateConnectionString(DbFileName1);
}
refresh_labels();
}
}

Entity Framework 6 set connection string in code

I have a dll that uses the Entity Framework 6 to do some database operations. I'm using a database first approach.
The model and everything concerning the Entity Framework, like the connection string in the App.config, were created via the wizzard in Visual Studio.
So I compiled the dll and put it together with the corresponding .config in the folder where the application using the dll expects it.
Everything works fine until I get to the point where an actual database call is made. There I get the error:
Cannot find connection string for MyDatabaseEntity
The automatically generated connectionstring is, as I said, in the config file of the dll. I cannot change the App.config of the application.
But the application hands over an object that has all the information I need to build the connection string myself.
So I'm looking for a way to set the connection string in the code without relying on a config file.
All the tutorials I find for a database first approach use this method though.
I found a post here that says to simply give the connection string as a parameter when creating the Object like
MyDatabaseEntities = new MyDatabaseEntities(dbConnect);
but ´MyDatabaseEntities´ doesn't have a constructor that takes any parameters
public partial class MyDatabaseEntities : DbContext
{
public MyDatabaseEntities()
: base("name=MyDatabaseEntities")
{
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
throw new UnintentionalCodeFirstException();
}
public virtual DbSet<MyTable> MyTable { get; set; }
}

How about:
public partial class MyDatabaseEntities : DbContext
{
public MyDatabaseEntities(string connectionString)
: base(connectionString)
{
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
throw new UnintentionalCodeFirstException();
}
public virtual DbSet<MyTable> MyTable { get; set; }
}
Then initialize your database like you did before:
string myConnectionString = "...";
MyDatabaseEntities = new MyDatabaseEntities(myConnectionString);

I had the similar issue. My Edmx and App.Config was in a different project. My startup project was different, had 3 different connection strings, we need to choose one on the fly depending on the environment. So couldn't use a fixed connection string. I created a partial class overload of the Context.cs using the same namespace. Following was my default Context.cs;
namespace CW.Repository.DBModel
{
public partial class CWEntities : DbContext
{
public CWEntities()
: base("name=CWEntities")
{
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
throw new UnintentionalCodeFirstException();
}
...
...
}
}
My partial class overload;
namespace CW.Repository.DBModel
{
public partial class CWEntities : DbContext
{
public CWEntities(string ConnectionString)
: base(ConnectionString)
{
}
}
}
Lastly, as my connection strings were not for EF, I converted them to a EF connection string.
public static string GetEntityConnectionString(string connectionString)
{
var entityBuilder = new EntityConnectionStringBuilder();
// WARNING
// Check app config and set the appropriate DBModel
entityBuilder.Provider = "System.Data.SqlClient";
entityBuilder.ProviderConnectionString = connectionString + ";MultipleActiveResultSets=True;App=EntityFramework;";
entityBuilder.Metadata = #"res://*/DBModel.CWDB.csdl|res://*/DBModel.CWDB.ssdl|res://*/DBModel.CWDB.msl";
return entityBuilder.ToString();
}
Lastly, the calling
var Entity = new CWEntities(CWUtilities.GetEntityConnectionString(ConnectionString));

I got this solution using below code, I can hardcode connection string using C# code without using config file.
public class SingleConnection
{
private SingleConnection() { }
private static SingleConnection _ConsString = null;
private String _String = null;
public static string ConString
{
get
{
if (_ConsString == null)
{
_ConsString = new SingleConnection { _String = SingleConnection.Connect() };
return _ConsString._String;
}
else
return _ConsString._String;
}
}
public static string Connect()
{
//Build an SQL connection string
SqlConnectionStringBuilder sqlString = new SqlConnectionStringBuilder()
{
DataSource = "SIPL35\\SQL2016".ToString(), // Server name
InitialCatalog = "Join8ShopDB", //Database
UserID = "Sa", //Username
Password = "Sa123!##", //Password
};
//Build an Entity Framework connection string
EntityConnectionStringBuilder entityString = new EntityConnectionStringBuilder()
{
Provider = "System.Data.SqlClient",
Metadata = "res://*/ShopModel.csdl|res://*/ShopModel.ssdl|res://*/ShopModel.msl",
ProviderConnectionString = #"data source=SIPL35\SQL2016;initial catalog=Join8ShopDB2;user id=Sa;password=Sa123!##;"// sqlString.ToString()
};
return entityString.ConnectionString;
}
and using DbContext using like this:
Join8ShopDBEntities dbContext = new Join8ShopDBEntities(SingleConnection.ConString);

Thanks a lot . I changed little for Code First EF6.
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data.Entity.Core.EntityClient;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Data
{
public class SingleConnection
{
private SingleConnection() { }
private static SingleConnection _ConsString = null;
private String _String = null;
public static string ConString
{
get
{
if (_ConsString == null)
{
_ConsString = new SingleConnection { _String = SingleConnection.Connect() };
return _ConsString._String;
}
else
return _ConsString._String;
}
}
public static string Connect()
{
string conString = ConfigurationManager.ConnectionStrings["YourConnectionStringsName"].ConnectionString;
if (conString.ToLower().StartsWith("metadata="))
{
System.Data.Entity.Core.EntityClient.EntityConnectionStringBuilder efBuilder = new System.Data.Entity.Core.EntityClient.EntityConnectionStringBuilder(conString);
conString = efBuilder.ProviderConnectionString;
}
SqlConnectionStringBuilder cns = new SqlConnectionStringBuilder(conString);
string dataSource = cns.DataSource;
SqlConnectionStringBuilder sqlString = new SqlConnectionStringBuilder()
{
DataSource = cns.DataSource, // Server name
InitialCatalog = cns.InitialCatalog, //Database
UserID = cns.UserID, //Username
Password = cns.Password, //Password,
MultipleActiveResultSets = true,
ApplicationName = "EntityFramework",
};
//Build an Entity Framework connection string
EntityConnectionStringBuilder entityString = new EntityConnectionStringBuilder()
{
Provider = "System.Data.SqlClient",
Metadata = "res://*",
ProviderConnectionString = sqlString.ToString()
};
return entityString.ConnectionString;
}
}
}

You can use singleton patter for it . For example
private YouurDBContext context;
public YouurDBContext Context
{
get
{
if (context==null)
{
context = new YouurDBContext();
}
return context;
}
set { context = value; }
}

Repeatedly creating and deleting databases in Entity Framework

When writing some unit tests for our application, I stumbled upon some weird behaviour in EF6 (tested with 6.1 and 6.1.2): apparently it is impossible to repeatedly create and delete databases (same name/same connection string) within the same application context.
Test setup:
public class A
{
public int Id { get; set; }
public string Name { get; set; }
}
class AMap : EntityTypeConfiguration<A>
{
public AMap()
{
HasKey(a => a.Id);
Property(a => a.Name).IsRequired().IsMaxLength().HasColumnName("Name");
Property(a => a.Id).HasColumnName("ID");
}
}
public class SomeContext : DbContext
{
public SomeContext(DbConnection connection, bool ownsConnection) : base(connection, ownsConnection)
{
}
public DbSet<A> As { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Configurations.Add(new AMap());
}
}
[TestFixture]
public class BasicTest
{
private readonly HashSet<string> m_databases = new HashSet<string>();
#region SetUp/TearDown
[TestFixtureSetUp]
public void SetUp()
{
System.Data.Entity.Database.SetInitializer(
new CreateDatabaseIfNotExists<SomeContext>());
}
[TestFixtureTearDown]
public void TearDown()
{
foreach (var database in m_databases)
{
if (!string.IsNullOrWhiteSpace(database))
DeleteDatabase(database);
}
}
#endregion
[Test]
public void RepeatedCreateDeleteSameName()
{
var dbName = Guid.NewGuid().ToString();
m_databases.Add(dbName);
for (int i = 0; i < 2; i++)
{
Assert.IsTrue(CreateDatabase(dbName), "failed to create database");
Assert.IsTrue(DeleteDatabase(dbName), "failed to delete database");
}
Console.WriteLine();
}
[Test]
public void RepeatedCreateDeleteDifferentName()
{
for (int i = 0; i < 2; i++)
{
var dbName = Guid.NewGuid().ToString();
if (m_databases.Add(dbName))
{
Assert.IsTrue(CreateDatabase(dbName), "failed to create database");
Assert.IsTrue(DeleteDatabase(dbName), "failed to delete database");
}
}
Console.WriteLine();
}
[Test]
public void RepeatedCreateDeleteReuseName()
{
var testDatabases = new HashSet<string>();
for (int i = 0; i < 3; i++)
{
var dbName = Guid.NewGuid().ToString();
if (m_databases.Add(dbName))
{
testDatabases.Add(dbName);
Assert.IsTrue(CreateDatabase(dbName), "failed to create database");
Assert.IsTrue(DeleteDatabase(dbName), "failed to delete database");
}
}
var repeatName = testDatabases.OrderBy(n => n).FirstOrDefault();
Assert.IsTrue(CreateDatabase(repeatName), "failed to create database");
Assert.IsTrue(DeleteDatabase(repeatName), "failed to delete database");
Console.WriteLine();
}
#region Helpers
private static bool CreateDatabase(string databaseName)
{
Console.Write("creating database '" + databaseName + "'...");
using (var connection = CreateConnection(CreateConnectionString(databaseName)))
{
using (var context = new SomeContext(connection, false))
{
var a = context.As.ToList(); // CompatibleWithModel must not be the first call
var result = context.Database.CompatibleWithModel(false);
Console.WriteLine(result ? "DONE" : "FAIL");
return result;
}
}
}
private static bool DeleteDatabase(string databaseName)
{
using (var connection = CreateConnection(CreateConnectionString(databaseName)))
{
if (System.Data.Entity.Database.Exists(connection))
{
Console.Write("deleting database '" + databaseName + "'...");
var result = System.Data.Entity.Database.Delete(connection);
Console.WriteLine(result ? "DONE" : "FAIL");
return result;
}
return true;
}
}
private static DbConnection CreateConnection(string connectionString)
{
return new SqlConnection(connectionString);
}
private static string CreateConnectionString(string databaseName)
{
var builder = new SqlConnectionStringBuilder
{
DataSource = "server",
InitialCatalog = databaseName,
IntegratedSecurity = false,
MultipleActiveResultSets = false,
PersistSecurityInfo = true,
UserID = "username",
Password = "password"
};
return builder.ConnectionString;
}
#endregion
}
RepeatedCreateDeleteDifferentName completes successfully, the other two fail. According to this, you cannot create a database with the same name, already used once before. When trying to create the database for the second time, the test (and application) throws a SqlException, noting a failed login. Is this a bug in Entity Framework or is this behaviour intentional (with what explanation)?
I tested this on a Ms SqlServer 2012 and Express 2014, not yet on Oracle.
By the way: EF seems to have a problem with CompatibleWithModel being the very first call to the database.
Update:
Submitted an issue on the EF bug tracker (link)

Database initializers only run once per context per AppDomain. So if you delete the database at some arbitrary point they aren't going to automatically re-run and recreate the database. You can use DbContext.Database.Initialize(force: true) to force the initializer to run again.

A few days ago I wrote integration tests that included DB access through EF6. For this, I had to create and drop a LocalDB database on each test case, and it worked for me.
I didn't use EF6 database initializer feature, but rather executed a DROP/CREATE DATABASE script, with the help of this post - I copied the example here:
using (var conn = new SqlConnection(#"Data Source=(LocalDb)\v11.0;Initial Catalog=Master;Integrated Security=True"))
{
conn.Open();
var cmd = new SqlCommand();
cmd.Connection = conn;
cmd.CommandText = string.Format(#"
IF EXISTS(SELECT * FROM sys.databases WHERE name='{0}')
BEGIN
ALTER DATABASE [{0}]
SET SINGLE_USER
WITH ROLLBACK IMMEDIATE
DROP DATABASE [{0}]
END
DECLARE #FILENAME AS VARCHAR(255)
SET #FILENAME = CONVERT(VARCHAR(255), SERVERPROPERTY('instancedefaultdatapath')) + '{0}';
EXEC ('CREATE DATABASE [{0}] ON PRIMARY
(NAME = [{0}],
FILENAME =''' + #FILENAME + ''',
SIZE = 25MB,
MAXSIZE = 50MB,
FILEGROWTH = 5MB )')",
databaseName);
cmd.ExecuteNonQuery();
}
The following code was responsible for creating database objects according to the model:
var script = objectContext.CreateDatabaseScript();
using ( var command = connection.CreateCommand() )
{
command.CommandType = CommandType.Text;
command.CommandText = script;
connection.Open();
command.ExecuteNonQuery();
}
There was no need to change database name between the tests.

Entity Framework: ObjectStateEntry error

I have code using entity framework as shown below. I am getting the following excpetion. What is the reason for this? How to overcome this?
The ObjectStateManager does not contain an ObjectStateEntry with a reference to an object of type 'MyEntityDataModelEDM.Payment'.
Note: I wrote this code based on the reply in Context Per Request: How to update Entity
CODE
public class MyPaymentRepository
{
private string connectionStringVal;
public MyPaymentRepository()
{
SqlConnectionStringBuilder sqlBuilder = new SqlConnectionStringBuilder();
sqlBuilder.DataSource = ".";
sqlBuilder.InitialCatalog = "LibraryReservationSystem";
sqlBuilder.IntegratedSecurity = true;
// Initialize the EntityConnectionStringBuilder.
EntityConnectionStringBuilder entityBuilder = new EntityConnectionStringBuilder();
entityBuilder.Provider = "System.Data.SqlClient";
entityBuilder.ProviderConnectionString = sqlBuilder.ToString();
entityBuilder.Metadata = #"res://*/MyEDMtest.csdl|res://*/MyEDMtest.ssdl|res://*/MyEDMtest.msl";
connectionStringVal = entityBuilder.ToString();
}
public MyEntityDataModelEDM.Payment GetPaymentByID(int paymentID)
{
MyEntityDataModelEDM.Payment payment;
using (var myDatabaseContext = new MyEntityDataModelEDM.LibraryReservationSystemEntities(connectionStringVal))
{
Func<MyEntityDataModelEDM.Payment, bool> predicate = (p => p.PaymentID == paymentID);
payment = myDatabaseContext.Payments.SingleOrDefault(predicate);
}
return payment;
}
public void UpdateDBWithContextChanges(MyEntityDataModelEDM.Payment paymentEntity)
{
using (var myDatabaseContext = new MyEntityDataModelEDM.LibraryReservationSystemEntities(connectionStringVal))
{
myDatabaseContext.ObjectStateManager.ChangeObjectState(paymentEntity, System.Data.EntityState.Modified);
myDatabaseContext.SaveChanges();
}
}
}
CLIENT
static void Main(string[] args)
{
MyRepository.MyPaymentRepository rep = new MyRepository.MyPaymentRepository();
MyEntityDataModelEDM.Payment p2 = rep.GetPaymentByID(1);
p2.PaymentType = "CHANGE";
rep.UpdateDBWithContextChanges(p2);
}
REFERENCE:
The ObjectStateManager does not contain an ObjectStateEntry with a reference to an object

You did not attach it to the context first. See the answer to the referenced question.