Question

I have two GridViews. I’ve got method GetGeneralDiagnosis which returns a list of all diagnosis:

CODE DIAGNOSIS
F50 Eating disorders
F51 Nonorganic sleep disorders

and method GetSpecificDiagnosis which returns more specific list:

CODE DIAGNOSIS
F50.0 Anorexia nervosa
F50.1 Atypical anorexia nervosa
F51.0 Nonorganic insomnia
F51.1 Nonorganic hypersomnia

Now I’ve got method which bind SPECIFIC DIAGNOSIS to second GridView according to GENERAL DIAGNOSIS from first GridView.

protected void gvGeneralDiagnosis_SelectedIndexChanged(object sender, EventArgs e)
{
    string generalDiagnosis = gvGeneralDiagnosis.DataKeys[gvGeneralDiagnosis.SelectedIndex].Values["ICD10Code"].ToString(); 
    var ICD10 = Visit.GetSpecificDiagnosis();   // here I'm getting data from database
    gvSpecificDiagnosis.DataSource = ICD10.Where(i => i.ICD10Code.Contains(generalDiagnosis)).Select(i => new { i.ICD10Name, i.ICD10Code });
    gvSpecificDiagnosis.DataBind();
}

I don’t want to connect to database each time selected index is changed.

How can i get my list var ICD10 = Visit.GetSpecificDiagnosis() only once? I heard that global variables are very bad idea, so how can I do that in another way?

Answer 1

You can use a private member variable. This one “lives” as long as the class containing it lives. Wrap it with a property to access it and automatically read it from the database, if necessary.

private TypeOfICD10 _icd10;
private TypeOfICD10 ICD10
{
    get
    {
        if (_icd10 == null) { // Get from database.
            _icd10 = Visit.GetSpecificDiagnosis();   
        }
        return _icd10;
    }
}

Now you can use it like this and it will be read from the db only at the first call

protected void gvGeneralDiagnosis_SelectedIndexChanged(object sender, EventArgs e)
{
    string generalDiagnosis = gvGeneralDiagnosis.DataKeys[gvGeneralDiagnosis.SelectedIndex].Values["ICD10Name"].ToString();
    gvSpecificDiagnosis.DataSource = ICD10
        .Where(i => i.ICD10Code.Contains(generalDiagnosis))
        .Select(i => new { i.ICD10Name, i.ICD10Code });
    gvSpecificDiagnosis.DataBind();
}