Entity Framework Core LINQ query with multiple where clauses

Question

I need some sample code for my project. I am working with EF CORE 2.1.1.

I created a function which accepts 3 parameters, inside that function I am executing a LINQ (lambda expression query), returning a list.

Here is my function :

public IEnumerable<Donneesource> GetAllSourcesFromBDD(DateTime PremierDateCom, DateTime DerniereDateCom, string Secteur)
{
    try
    {
        //Récupération des données.
             IEnumerable<Donneesource> RawDatas = _sourceDAL.Donneesource
                .Where(ic => ic.EstCopieDestination == false)
                .Where(s => PremierDateCom != DateTime.MinValue && s.SComPremierDate.Value.Date == PremierDateCom.Date)
                .Where(s => DerniereDateCom != DateTime.MinValue && s.SComDerniereDate.Value.Date == DerniereDateCom.Date)                    
                .Where(s => Secteur != string.Empty && s.SSectNom == Secteur)
                .ToList();

        return RawDatas;              
    }
    catch(Exception)
    { 
        return null;
    }
}

By default I set DateTime params to DateTime.MinValue (PremierDateCom,DerniereDateCom) and string param to string.Empty (Secteur).

I am trying to create a single query with where clauses. I want to ignore the where clauses with default params. For example If PremierDateCom = DateTime.MinValue (or other params) then I want to ignore the where clauses if something I want to include my where clause in my query.

I don't want to create a query like this:

  //Filtre
            if (PremierDateCom != DateTime.MinValue)
                RawDatas = RawDatas.Where(x => x.SComPremierDate.Value.ToShortDateString() == PremierDateCom.ToShortDateString());
            //Filtre
            if (DerniereDateCom != DateTime.MinValue)
                RawDatas = RawDatas.Where(x => x.SComDerniereDate.Value.ToShortDateString() == DerniereDateCom.ToShortDateString());   
            //Filtre                
            if (Secteur != null)
                RawDatas = RawDatas.Where(x => x.SSectNom == Secteur);

Answer 1

Assuming _sourceDAL.Donneesource gives you an IQueryable<T> then you should be building up your query by adding Where clauses inside an if statement. This is because an IQueryable will not run a query against the database until you materialise it, i.e. with a foreach or a .ToList(). So something like this:

IQueryable<Donneesource> RawDatas = _sourceDAL.Donneesource
    .Where(ic => ic.EstCopieDestination == false)
    .Where(s => PremierDateCom != DateTime.MinValue && s.SComPremierDate.Value.Date == PremierDateCom.Date)
    .Where(s => DerniereDateCom != DateTime.MinValue && s.SComDerniereDate.Value.Date == DerniereDateCom.Date)                    
    .Where(s => Secteur != string.Empty && s.SSectNom == Secteur);

if (PremierDateCom != DateTime.MinValue)
{
    RawDatas = RawDatas.Where(x => x.SComPremierDate.Value.ToShortDateString() == PremierDateCom.ToShortDateString());
}

if (DerniereDateCom != DateTime.MinValue)
{
    RawDatas = RawDatas.Where(x => x.SComDerniereDate.Value.ToShortDateString() == DerniereDateCom.ToShortDateString());   
}

if (Secteur != null)
{
    RawDatas = RawDatas.Where(x => x.SSectNom == Secteur);
}

//Now get the data from the database:

return RawDatas.ToList();

Answer 2

To avoid using many if statements you can also try the following:

IQueryable<Donneesource> RawDatas = _sourceDAL.Donneesource
.Where(ic => !ic.EstCopieDestination)
.Where(s => PremierDateCom != DateTime.MinValue ? s.SComPremierDate.Value.Date == PremierDateCom.Date : true)
.Where(s => DerniereDateCom != DateTime.MinValue ? s.SComDerniereDate.Value.Date == DerniereDateCom.Date : true)
.Where(s => Secteur != string.Empty ? s.SSectNom == Secteur : true);

You can use a conditional statement, and if the condition is not satisfied, pass true instead.