Abstract Linq method

Question

I have two different databases which were abstracted in Linqs through Linq4Templates: LINQA (LINQA.cs) and LINQB(LINQB.cs).They both have the same tables.

Whenever I want to use them, I need to do:

using (var dbA = new LinqA())
{      
   query = from a in dbA.Table1 
}
using (var dbB = new LinqB())
{      
   query = from a in dbB.Table1
}

How could I abstract those classes in a way I call them as generic and inside they the class could know if I'm using A or B?

for instance:

using (var db = new LinqDB("dbB"))
{      
   query = from a in db.Table1 
}

Answer 1

Hello,

Perhaps a DbContext factory as described here which talks about ASP.NET but should work for code first in a non ASP.NET project..

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NuGet BaseConnectionLibrary for database connections.

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Answer 2

The only abstraction you can do is make a custom class,   a container class, that represents both tables if the tables in two databases are the same, like a DTO.

https://www.codeproject.com/Articles/1050468/Data-Transfer-Object-Design-Pattern-in-Csharp

You can use a Linq projection and project into a custom type like a DTO.

https://csharp-station.com/Tutorial/Linq/Lesson02

Sure, you can make some custom class the has a means to accept a flag to indicate which database table to use, do the Linq projection into the DTO and return the DTO(s) in a collection Lst<DTO> out of the method.

Answer 3

Hi FcabralJ,

Thank you for posting here.

It seems that similar functionality can be achieved using reflection.

These codes may give you some ideas.

    class Program
    {
        static void Main(string[] args)
        {
            Type type = typeof(ClassA);
            ConstructorInfo magicConstructor = type.GetConstructor(Type.EmptyTypes);
            object magicClassObject = magicConstructor.Invoke(new object[] { });
            MethodInfo magicMethod = type.GetMethod("GetTable");
            object magicValue = magicMethod.Invoke(magicClassObject,null);

        }
    }

    class ClassA
    {
        public DataTable GetTable() 
        {
            using (SqlConnection conn = new SqlConnection(@"ConnString1"))
            {
                conn.Open();
                using (SqlCommand command = new SqlCommand("select * from emp",conn))
                {
                    SqlDataReader reader = command.ExecuteReader();
                    DataTable dataTable = new DataTable();
                    dataTable.Load(reader);
                    return dataTable;
                }
            }
        }
    }

    class ClassB
    {
        public DataTable GetTable()
        {
            using (SqlConnection conn = new SqlConnection(@"ConnString2"))
            {
                conn.Open();
                using (SqlCommand command = new SqlCommand("select * from emp", conn))
                {
                    SqlDataReader reader = command.ExecuteReader();
                    DataTable dataTable = new DataTable();
                    dataTable.Load(reader);
                    return dataTable;
                }
            }
        }
    }

Hope this could be helpful.

Best Regards,

Timon

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