实体框架选择查询

Question

I am making a simple application for insert, update, delete, select data with Entity Framework
I already made insertion, deletion and select all data.

Now I want to select with where condition with filter of two fields
For ex : I have table with

userid
username
password
email

Now need selection like where email = "" and password = ""

I know how to write query in SQL but having not clues with entity framework .
Also need to store this result in datatable and looping solution both for learning purpose.
This can help many beginners

Answer 1

Using Linq To Entities with lambda expression:

var result = dBContext.Account.Where(a=> a.email == "" && a.password =="").ToList();

Using Linq To Entities the less fancy way:

var result = (from a in dBContext.Account
              where a.email == "" && a.password ==""
              select a).ToList();

Lambda expressions are used most of the time. Some people find lambda's less readable. I think it's more a personal taste that depends from your background.

EDIT:

dbContext should be replaced by the name you gave your dbContext/Entities when setting up your Entitiy framework EDMX or Code First Classes.

Account should be replaced by the name of your table/Entity

To loop and edit the results you can do:

foreach(var account in results)
{
   //do something with the properties
   account.email = "test@updated.com"
}

//store the changes again in the db
dbContext.SaveChanges();

Answer 2

Use linq ex:

List<User> result = dbContext.Users.Where(o=> o.email == "" && o.password=="").ToList();

foreach(User u in result)
{
// do stuff
}

User u = new User();
u.Email = "mail@mail.com";

dbContext.Users.Add(u);
dbContext.Save(); //I think its Save()..

Answer 3

Have to use Linq query like

var data= dBContext.Account.Where(a=> a.email == "" && a.password =="").ToList();

.ToList() will give your entire data that comes under your where condition or filter. Now for that you return DataTable and easily apply a for condtion based on your DataTable values.

Answer 4

DataTable tempData = (DataTable)grdRecords.DataSource;

var query = from r in tempData.AsEnumerable()
            where r.Field<string>("UserName") != "TestUsername" &&
                  r.Field<string>("Password") != "TestPassword"
            select r;

DataTable newDT = query.CopyToDataTable();

Answer 5

use linq query as follows

IList<Users> Users = dbContext.Users.Where(x=> x.email == "" && x.password=="").ToList();

then if you want to convert into DataTable just call following generic method do convert it

        public DataTable ToDataTable<T>(IList<T> data)// T is any generic type
        {
            PropertyDescriptorCollection props = TypeDescriptor.GetProperties(typeof(T));

            DataTable table = new DataTable();
            for (int i = 0; i < props.Count; i++)
            {
                PropertyDescriptor prop = props[i];
                table.Columns.Add(prop.Name, prop.PropertyType);
            }
            object[] values = new object[props.Count];
            foreach (T item in data)
            {
                for (int i = 0; i < values.Length; i++)
                {
                    values[i] = props[i].GetValue(item);
                }
                table.Rows.Add(values);
            }
            return table;
        }

Answer 6

You can try this

databasenameEntities db = new databasenameEntities ();

tablename exist= db.tablename.where(p=>p.email=="txtemail.text" && p.password=="txtpassword.text");

if(exist.count>0)

{

txtuserid.text=Convert.toInt32(exist.userid);

txtusername.Text=exist.username;

....

.....

db.saveChanges();

}

hope this may helpful.