在C＃中加入3个数据表

Question

I have the following 3 data-tables:

    Table1 
    --------------------------------
    ScheduleID | Name  | Details
    -----------------------------
    1             S1     schedule details 
    2             S2     schedule details
    3             S3     schedule details
    4             S4     schedule details


    Table2
    ------------------------------
    ScheduleGroupID  | ScheduleID 
    ------------------------------
    1                      1      
    1                      2    
    1                      3     
    2                      4     

    Table3
    -----------------------------------------------
    ScheduleGroupID   | Description  | ScheduleCount
    ------------------------------------------------
    1                    Urgent             3
    2                    Non-urgent         1


    Expected Result
    ---------------------------------------------------------------
    ScheduleID | Name | Details | ScheduleGroupID |   Description
    -------------------------------------------------------------
    1             S1       5             1         Urgent(row from table3) 
    2             S2       5             1         Urgent(row from table3) 
    3             S3       5             1         Urgent(row from table3) 
    4             S4       5             2         Non-urgent(from table3) 

So i have three datatables and would like to merge them into one table in order to produce the expected result shown above. How can this be done within c#? I assume i would have to use LINQ but don't have much experience with it.

Answer 1

You can do like this create a class like below

public class TestClass
{
    public int ScheduleID { get; set; }
    public string Name { get; set; }
    public string Details { get; set; }
    public int ScheduleGroupID { get; set; }
    public string Description { get; set; }
}

And write the query like this

List<TestClass> colection = (from x in db.Table1
                join y in db.Table2 on x.ScheduleID  equals y.ScheduleID
                join z in db.Table3 on y.ScheduleGroupID equals z.ScheduleGroupID
                select new CityClass
                {
                   ScheduleID = x.ScheduleID,
                   Name = x.Name,
                   Details  = x.Details,
                   ScheduleGroupID = y.ScheduleGroupID,
                   Description = z.Description
                }).ToList();

Answer 2

Assuming it is DataTable you could join this way.

    var result = from s in schedule.AsEnumerable()
    join sg in  schedulegroup.AsEnumerable() on s.Field<int>("ScheduleID") equals sg.Field<int>("ScheduleID") 
    join g in groups.AsEnumerable() on sg.Field<int>("ScheduleGroupID") equals g.Field<int>("ScheduleGroupID") 
    select new 
    {
        ScheduleID = s.Field<int>("ScheduleID"),
        Name = s.Field<string>("Name"),
        Details = s.Field<int>("Details"),
        ScheduleGroupID = sg.Field<int>("ScheduleGroupID"),
        Description = g.Field<string>("Description")
    };

Check this Demo

Answer 3

The question you are asking is 2 parts

first connecting to the database

As you have stated that you want to avoid EnitiyFramework

some of the other options are

• LinqToSql :this will function fairly similar to EF with out all the overhead of the full framework

• if you want to go back and be even more old school you have datasets which can be configured to be more useful than a generic dataset

• or even more old school SQLCommands and datareaders

once you have the data

then the best method of querying is LinqToObjects

var results = from a in Table1
              join b in Table2 on a.ID equals b.ID
              join c in Table3 on b.ID2 equals c.ID2
              //create a anonymous type or better if you want the results to persist create a normal object
              select new{ a.Column1, a.Column2, b.Column1, c.Column1};

failing that you can do it via code eg

//firstly build up a key index to make the matching easier
var t1Dic = new Dictionary<int,DataRow>();
foreach(var row in table1.Rows)
{
    t1Dic.Add(row[IDCol],row);
}
var t2Dic = new Dictionary<int,DataRow>();
foreach(var row in table2.Rows)
{
    t2Dic.Add(row[IDCol],row);
}
//next run though your linking table and add them to your results table
var results = new DataTable();
foreach(var row in table3.Rows)
{
    var r = results.NewRow();
    r[YourColumnName1] = t1Dic[row[Id1Col][YourColumnName1];
    r[YourColumnName2] = t1Dic[row[Id1Col][YourColumnName2];
    r[YourColumnName3] = t2Dic[row[Id2Col][YourColumnName3];
    r[YourColumnName4] = t2Dic[row[Id2Col][YourColumnName4];
    r[YourColumnName5] = t2Dic[row[Id2Col][YourColumnName5];
}

EF and Linq are definitely the easiest method though

Answer 4

Bringing direct relationship between tables would make easier for the program to retrieve data. If EF is used, results can be retrieved by writing a single line.

Above tables can be changed to use only 2 tables . You can add another column in table1 as schedulegroupID which would be foreign key to schedulegroup table

ALTER TABLE dbo.schedule
ADD schedulegroupId INT

ALTER TABLE dbo.schedule
ADD CONSTRAINT FK_scheduleGroup
FOREIGN KEY (schedulegroupId)
REFERENCES scheduleGroup(ID)

In this way, there would be direct relationship between the tables which makes it easier to write both SQL and LINQ queries.

--SQL Query 
SELECT * FROM dbo.schedule s INNER JOIN dbo.scheduleGroup sg ON s.schedulegroupid = sg.ID
//LINQ Query    
var query = db.schedules.Include("scheduleGroup").ToList();

Below code would show the first line of the required results.

Console.WriteLine(query[0].Name.ToString() + "," +  query[0].Details.ToString() + "," +  query[0].schedulegroupId.Value.ToString() + ","
                + query[0].scheduleGroup.Description.ToString());