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c#entity-framework
John Matthews
John Matthews

Reputation: 75

Avoid a lot of if - else checks - Choose table from string using the entity framework

I'm developing an app with Entity Framework. I've got a combo box with the names of the tables in the database. I have the following code:

string table = cbTables.SelectedItem.ToString();
using (var dbContext = new Entities()) {
    if (table.Equals("Person")) {
        List<Person> list = (from l in dbContext.People select l).ToList();
    } else if (table.Equals("Student")) {
        List<Student> list = (from u in dbContext.Student select u).ToList();
    } else if (table.Equals("Grade")) {
        List<Grade> list = (from p in dbContext.Grade select p).ToList();
}

how can i avoid all these if-else checks? Is it possible to get the name of a class from a string holding the name?

example:

string = "Person";
var str = //something
List<str> list = (from u in dbContext.str select u).ToList();

Upvotes: 6

Views: 266

Answers (4)

Ali Umair
Ali Umair

Reputation: 1424

Why aren't you using Switch for this purpose? 

string table = cbTables.SelectedItem.ToString();

using (var dbContext = new Entities()) 
{
    switch (table)
    {
        case"Person":
            List<Person> list = (from l in dbContext.People select l).ToList();
            break;
        case"Student":
            List<Student> list = (from u in dbContext.Student select u).ToList();
            break;
        case"Grade":
            List<Grade> list = (from p in dbContext.Grade select p).ToList();
            break;
    }
}

Upvotes: 0

tia
tia

Reputation: 9698

ComboBox is capable of displaying dictionary through the datasource, so you can bind display text with the data you actually want instead of checking the display text. Then in this case we would bind it to the type of the entity:

Dictionary<string,Type> typeMap = new Dictionary<string,Type> {
    { "Person", typeof(Person) },
    { "Student", typeof(Student) },
    { "Grade", typeof(Grade) },
}

then bind it to ComboBox like:

cbTables.DataSource = new BindingSource(typeMap, null);
cbTables.DisplayMember = "Key";
cbTables.ValueMember = "Value";

then, when you need to get selected entity, use

Type entityType = (Type) cbTables.SelectedValue;
DbSet set = dbContext.Set(entityType);

However, after this you need to inspect entityType and display the form accordingly. If your form needs List e.g. List, then use

List<Student> studentList = set.Cast<Student>.ToList();

Upvotes: 2

sq33G
sq33G

Reputation: 3360

To expand on my comment:

You can declare a dictionary to map from the string of your table name to the actual DbSet that is your table:

string table = cbTables.SelectedItem.ToString();
using (var dbContext = new Entities()) {
    Dictionary<string, DbSet> mapping = new Dictionary<string, DbSet> {
        { "Person", dbContext.Person },
        { "Student", dbContext.Student },
        { "Grade", dbContext.Grade }
    };

    //...

The problem will remain - what to do with your result set? Right now you have typed lists with the specific type of each table's members; you won't be able to do that without a decision (if/switch) of some sort.

Upvotes: 1

Ron Sijm
Ron Sijm

Reputation: 8738

Assuming you don't want a switch but you want something dynamic, you can use queries instead:

using (var context = new Context())
{
    var people = context.Database.SqlQuery<Object>(
                       "select * from People").ToList();
}

Upvotes: 1

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