Question

I’m having a Entity-Set Countries, reflecting a database table ‘<‘char(2),char(3),nvarchar(50> in my database.

Im having a parser that returns a Country[] array of parsed countries, and is having issues with getting it updated in the right way. What i want is: Take the array of countries, for those countries not already in the database insert them, and those existing update if any fields is different. How can this be done?

void Method(object sender, DocumentLoadedEvent e)
{
    var data = e.ParsedData as Country[];
    using(var db = new DataContractEntities)
    {
       //Code missing

    
    }
}

I was thinking something like

for(var c in data.Except(db.Countries)) but it wount work as it compares on wronge fields.

Hope anyone have had this issues before, and have a solution for me. If i cant use the Country object and insert/update an array of them easy, i dont see much benefict of using the framework, as from performers i think its faster to write a custom sql script that inserts them instead of ect checking if an country is already in the database before inserting?

Solution

See answer of post instead.

I added override equals to my country class:

    public partial class Country
{
    
    public override bool Equals(object obj)
    {
        if (obj is Country)
        {
            var country = obj as Country;
            return this.CountryTreeLetter.Equals(country.CountryTreeLetter);
        }
        return false;
    }
    public override int GetHashCode()
    {
        int hash = 13;
        hash = hash * 7 + (int)CountryTreeLetter[0];
        hash = hash * 7 + (int)CountryTreeLetter[1];
        hash = hash * 7 + (int)CountryTreeLetter[2];
        return hash;
    }
}

and then did:

        var data = e.ParsedData as Country[];
        using (var db = new entities())
        {
            foreach (var item in data.Except(db.Countries))
            {
                db.AddToCountries(item); 
            }
            db.SaveChanges();
        }

Answer 1

I would do it straightforward:

void Method(object sender, DocumentLoadedEvent e)
{
    var data = e.ParsedData as Country[];
    using(var db = new DataContractEntities)
    {
        foreach(var country in data)
        {
            var countryInDb = db.Countries
                .Where(c => c.Name == country.Name) // or whatever your key is
                .SingleOrDefault();
            if (countryInDb != null)
                db.Countries.ApplyCurrentValues(country);
            else
                db.Countries.AddObject(country);
        }
        db.SaveChanges();
     }
}

I don’t know how often your application must run this or how many countries your world has. But I have the feeling that this is nothing where you must think about sophisticated performance optimizations.

Edit

Alternative approach which would issue only one query:

void Method(object sender, DocumentLoadedEvent e)
{
    var data = e.ParsedData as Country[];
    using(var db = new DataContractEntities)
    {
        var names = data.Select(c => c.Name);
        var countriesInDb = db.Countries
            .Where(c => names.Contains(c.Name))
            .ToList(); // single DB query
        foreach(var country in data)
        {
            var countryInDb = countriesInDb
                .SingleOrDefault(c => c.Name == country.Name); // runs in memory
            if (countryInDb != null)
                db.Countries.ApplyCurrentValues(country);
            else
                db.Countries.AddObject(country);
        }
        db.SaveChanges();
     }
}