Category: App Services

We want to treat lambda expressions as expression trees and look inside them instead of executing them. For example, LINQ to SQL gets the expression and converts it to the equivalent SQL statement and submits it to server (rather than executing the lambda).

With Lambda expressions we can write less code, and the code will be more readable.

A lambda expression uses the lambda operator => which means goes to.

arguments => expession

The expression reads: arguments goes to expression.

Let’s start with a common example;

using System;

namespace Lambdas
{
    class Program
    {
        static void Main()
        {
            Console.WriteLine(Square(5));
            Console.ReadLine();
        }

        static int Square(int num)
        {
            return num * num;
        }
    }
}

we declare a method called Square of type int with one input parameter of type int. It multiplies the number and returns the result.

In the Main() method we call our Square method with an int as a parameter.

We can convert this function into a Lambda expression. This is what it would look like:

num => num * num;

This expression would read: num goes to calculation (num * num).

This expression is short and easily readable once we get used to it. The catch though, is that a Lambda expression must be assigned to a delegate.

Resources

https://stackoverflow.com/questions/793571/why-would-you-use-expressionfunct-rather-than-funct

https://tyrrrz.me/blog/expression-trees

https://thesharperdev.com/an-introduction-to-c-expression-trees/

Midnight is the first one – It’s the very first second of the day, not the last.

var todayDateTime = DateTime.Today;
var Midnight = todayDateTime.AddSeconds(-1);
//Here are the results
Console.WriteLine($"Today {todayDateTime.ToString()}, Mid night {Midnight.ToString()}");

The output is this;

Today 10/8/2021 12:00:00 AM, Mid night 10/7/2021 11:59:59 PM

I am using EF for most of my ORM and data access. Recently I have tries Dapper and started liking it because of its simplicity and small footprint. Here is a list of example;

Using Dapper to fill a dataset;

Dapper returns a IDataReader when we use the ExecuteReaderAsync method. More information on this addition can be found here and here.

Use Nuget package to add Dapper. Add this to your Main class for quick demo;

static IDbConnection dbConn = new SqlConnection(ConfigurationManager.ConnectionStrings["SqlServerConnString"].ConnectionString);

Here you go with DataSet example using Dapper;

public async Task<DataSet> GetUserInformationOnUserId(int UserId)
{
    var storedprocedure = "usp_getUserInformation";
    var param = new DynamicParameters();
    param.Add("@userId", UserId);
    var list = await SqlMapper.ExecuteReaderAsync(dbConn, storedprocedure, param, commandType: CommandType.StoredProcedure);
    var dataset = ConvertDataReaderToDataSet(list);
    return dataset;
}

Here is conversion to dataset method;

public DataSet ConvertDataReaderToDataSet(IDataReader data)
{
    DataSet ds = new DataSet();
    int i = 0;
    while (!data.IsClosed)
    {
        ds.Tables.Add("Table" + (i + 1));
        ds.EnforceConstraints = false;
        ds.Tables[i].Load(data);
        i++;
    }                    
    return ds;
}

How to map class names to class properties with dapper

Manually map column name with class properties

Does Dapper supports .NET DataSets