动态LINQ可枚举选择

Question

I have the following bool Variables:

    public bool bCompanyID { get; set; }
    public bool bTaxCode { get; set; }
    public bool bAccountCode { get; set; }

Depending on which ones are set to true I set the LINQ expression (this is an example where all three are true :

System.Collections.Generic.IEnumerable<IP_DataRow> items = null;
items = _vm.Result_Error.Where(n => n.CompanyID == SelectedItem.CompanyID && n.TaxCode == SelectedItem.TaxCode && n.AccountCode == SelectedItem.AccountCode);

What I would like to do (rather than using multiple if statements) is to create this expression dynamically based on the user input.

Is something like this possible, or I simply have to use if statements?

EDIT:

Here is what came to my mind:

                items = _vm.Result_Error.Where(n => ((bCompanyID) ? (n.CompanyID == SelectedItem.CompanyID) : true) && 
                                                    ((bTaxCode) ? (n.TaxCode == SelectedItem.TaxCode) : true) &&
                                                    ((bAccountCode) ? (n.AccountCode == SelectedItem.AccountCode) : true));

Can I use the above mentioned expression?

Answer 1

Well you can combine then into one using something like this:

System.Collections.Generic.IEnumerable<IP_DataRow> items = null;
items = _vm.Result_Error.Where(n => (!bCompanyID    || n.CompanyID == SelectedItem.CompanyID)
                                 && (!bTaxCode      || n.TaxCode == SelectedItem.TaxCode)
                                 && (!bAccountCode  || n.AccountCode == SelectedItem.AccountCode));

but an if statement might be cleaner, especially since you can attach multiple where clauses to an existing query:

items = _vm.Result_Error.AsEnumerable();
if(bCompanyID)
    items = items.Where(n => n.CompanyID == SelectedItem.CompanyID);
if(bTaxCode)
    items = items.Where(n => n.TaxCode == SelectedItem.TaxCode);
if(bAccountCode)
    items = items.Where(n =>n.AccountCode == SelectedItem.AccountCode);

Answer 2

You can combine some conditions with if statements:

var items = _vm.Result.Errors;
if (bCompanyID)
    items = items.Where(n => n.CompanyID == SelectedItem.CompanyID);

if (bTaxCode)
    items = items.Where(n => n.TaxCode == SelectedItem.TaxCode);

. . .

You can also create single LINQ expression that (as I think) is not so effective:

var items = from item in _vm.Result.Errors
            where !bCompanyID || item.CompanyID == SelectedItem.CompanyID
            where !bTaxCode || item.TaxCode == SelectedItem.TaxCode
            . . .
            select item;

In the second case the lazy evaluating of && and || operators is used, so if bCompanyID is false , then right conditions will not evaluating.