C# - LINQ - specific query select-CodePudding

I would like to get a specific select with the best performance possible

I currently have a code like this:

var getData = from x in dbContex.MyTable
                                            where x.Car == "audi"
                                            select x;

MyTable has three columns: Car ProductionYear Color

I would like to download a specific vehicle brand with the year of manufacture that has a specific color.

I am currently doing it with reference to the code above:

 foreach (var item in getData)
                {
                    if (item.color == "blue") item.ProductionYear = "1999";
                    if (item.color == "red") item.ProductionYear = "2003";

        // etc (...)
                }

I would like to assign a specific year for a given car and color if I find it.

A very prosaic example above.

Problem - I currently have 100 colors and only want to check 10 colors.

How can I do it faster so as not to search the entire list and not to use IF statements?

CodePudding user response：

Create an array of the colors, then use Contains method in the predicate expression:

var colors = new [] { "red", "blue" };

var results = dbContext.MyTable
    .Where( x => "audi" == x.Car
        && colors.Contains( x.color ) );

Then use a switch statement to assign your years:

foreach(var car in results)
{
    car.ProductionYear = car.color switch
    {
        "blue" => 1999,
        "red" => 2003,
        _ => // unexpected result, throw exception
    }
}

You could also define the years with the colors then work the year assignment into the LINQ query:

var colorYears = new []
{
    new {
        color = "red",
        ProductionYear = 2003,
    },
    ...
};

var colors = colorYears.Select( x => x.color ).ToArray();

var results = (...query from above...)
    // enumerate
    .ToArray()
    // join datasource results with your colorYears array
    // on the `color` property
    .Join( colorYears, 
        c => c.color, 
        cy => cy.color,
        ( c, cy ) => 
        {
            // assign the configured production year for the color
            c.ProductionYear = cy.ProductionYear;
            // return the entity
            return c;
        } );

CodePudding user response：

There is no scenario, where you don`t use if or switch clause. You want to change data, which is not LINQ case. Only thing I would do - go to switch, rather than If clause.