I'm using SQL Server 2005. I have a table scores with 6 rows and columns - name, score and id.
I added the data source with VS and it generated a dataset called testDataSet.
So I tried the following code which gives me zero results:
testDataSet db = new testDataSet();
var result = from row in db.scores
select row.name;
Where is the problem?
The probem you are having is that you are querying an empty DataSet.
You first have to create a connection to your testDataSet and fill the tables contained in it with data from your database.
If you have created testDataSet with the automated tools VS provides then the tool will have also created the relevant TableDataAdapters (in their own namespace) to fill and update your DataSet.
Initialize the relevant TableDataAdapter and fetch the data from the database with the Fill(db) method.
you sould query dataTable like this:
DataTable products = ds.Tables["Product"];
var query = products.AsEnumerable().
Select(product => new
{
ProductName = product.Field<string>("Name"),
ProductNumber = product.Field<string>("ProductNumber"),
Price = product.Field<decimal>("ListPrice")
});
Try this code instead:
scoresTableAdapter adapter = new scoresTableAdapter();
var result = from row in adapter.GetData() select row.name;
Others are right that your problem is that you are not querying the data. When you generated the dataset, an adapter is also generated for you, that will help you to query the data as shown above.
The DataSet is just a structured container for the query results, it has no connection to the data source (database). In order to populate the DataSet with data you need to use a DataAdapter with a SelectCommand and call the Fill method.
var myConn = new SqlConnection ("..." );
var myAdapter = new SqlDataAdapter ( "SELECT * FROM TableName", myConn );
var myData = new testDataSet( );
myAdapter.Fill ( myData, "TableName" );
Related
I did a search and found some seemingly related answers, but they don't really do what I'm after.
Given a valid connection string and a table name, I want to get a DataTable of the table. I.e. if the table has a column called "Name", I want the DataTable set up so I can do dt["Name"] = "blah";
The trick is, I don't want to hard code any of that stuff, I want to do it dynamically.
People tell you to use SqlConnection.GetSchema, but that gives you back a table with a bunch of stuff in it.
Everybody has random tricks like TOP 0 * from the table and get the schema from there, etc.
But is there a way to get the table with the primary keys, unique indexes, etc. Ie.. in the final format to do a bulk insert.
You can use SqlDataAdapter.FillSchema:
var connection = #"Your connection string";
var command = "SELECT * FROM Table1";
var dataAdapter = new System.Data.SqlClient.SqlDataAdapter(command, connection);
var dataTable = new DataTable();
dataAdapter.FillSchema(dataTable, SchemaType.Mapped);
This way you will have an empty DataTable with columns and keys defined and ready to use in code like dataTable["Name"] = "blah";.
I have a table which has some 100-200 records.
I have fetch those records into a dataset.
Now i am looping through all the records using foreach
dataset.Tables[0].AsEnumerable()
I want to update a column for each record in the loop. How can i do this. Using the same dataset.
I'm Assumng your using a Data Adapter to Fill the Data Set, with a Select Command?
To edit the data in your Data Table and save changes back to your database you will require an Update Command for you Data Adapter. Something like this :-
SQLConnection connector = new SQLConnection(#"Your connection string");
SQLAdaptor Adaptor = new SQLAdaptor();
Updatecmd = new sqlDbCommand("UPDATE YOURTABLE SET FIELD1= #FIELD1, FIELD2= #FIELD2 WHERE ID = #ID", connector);
You will also need to Add Parameters for the fields :-
Updatecmd.Parameters.Add("#FIELD1", SQLDbType.VarCHar, 8, "FIELD1");
Updatecmd.Parameters.Add("#FIELD2", SQLDbType.VarCHar, 8, "FIELD2");
var param = Updatecmd.Parameters.Add("#ID", SqlDbType.Interger, 6, "ID");
param.SourceVersion = DataRowVersion.Original;
Once you have created an Update Command with the correct SQL statement, and added the parameters, you need to assign this as the Insert Command for you Data Adapter :-
Adaptor.UpdateCommand = Updatecmd;
You will need to read up on doing this yourself, go through some examples, this is a rough guide.
The next step is to Enumerate through your data table, you dont need LINQ, you can do this :-
foreach(DataRow row in Dataset.Tables[0].Rows)
{
row["YourColumn"] = YOURVALUE;
}
One this is finished, you need to call the Update() method of yout Data Adapter like so :-
DataAdapter.Update(dataset.Tables[0]);
What happens here, is the Data Adapter calls the Update command and saves the changes back to the database.
Please Note, If wish to ADD new rows to the Database, you will require am INSERT Command for the Data Adapter.
This is very roughly coded out, from the top of my head, so the syntax may be slightly out. But will hopefully help.
You should use original DataAdapter (adapter in code below) that was used to fill DataSet and call Update method, you will need CommandBuilder also, it depends what DB you are using, here is the example for SQL server :
SqlCommandBuilder builder = new SqlCommandBuilder(adapter);
adapter.UpdateCommand = builder.GetUpdateCommand();
adapter.Update(dataset);
dataset.AcceptChanges();
Here is the good example :
http://support.microsoft.com/kb/307587
The steps would be something like:
- create a new DataColumn[^]
- add it to the data table's Columns[^] collection
- Create a DataRow [^] for example using NewRow[^]
- Modify the values of the row as per needed using Item[^] indexer
- add the row to Rows[^] collection
- after succesful modifications AcceptChanges[^]
Like this:
DataTable table = new DataTable();
table.Columns.Add("ID", typeof(int));
table.Columns.Add("ProductName");
table.Rows.Add(1, "Chai");
table.Rows.Add(2, "Queso Cabrales");
table.Rows.Add(3, "Tofu");
EnumerableRowCollection<DataRow> Rows = table.AsEnumerable();
foreach (DataRow Row in Rows)
Row["ID"] = (int)Row["ID"] * 2;
Add the column like below.
dataset.Tables[0].Columns.Add(new DataColumn ("columnname"));
Update the columns values like below.
for (int i = 0; i <= ds.Tables[0].Rows.Count - 1; i++)
{
dataset.Tables[0].Rows[i]["columnname"] = "new value here";
}
Update Database
dataset.AcceptChanges();
I have the following method created and previously stock1Label to stock3Label were able to output the correct values from the database however after i added more rows to my ProductsTable, source.Rows[0][0], [1][0], etc. seems to be taking values from row 8 onwards of my table instead of row 1, anyone know why this is happening?
private void UpdateStocks()
{
string query = "SELECT pQty FROM ProductsTable";
OleDbDataAdapter dAdapter = new OleDbDataAdapter(query, DBconn);
DataTable source = new DataTable();
dAdapter.Fill(source);
stock1Label.Text = source.Rows[0][0].ToString();
stock2Label.Text = source.Rows[1][0].ToString();
stock3Label.Text = source.Rows[2][0].ToString();
stock4Label.Text = source.Rows[3][0].ToString();
stock5Label.Text = source.Rows[4][0].ToString();
stock6Label.Text = source.Rows[5][0].ToString();
}
Most (all?) database systems do not have defined orders.
You will receive rows in non-determinstic storage order, not in the order you inserted them.
To receive a meaningful consistent ordering, you need to add an ORDER BY clause.
I have a postgresql db and a C# application to access it. I'm having a strange error with values I return from a NpgsqlDataAdapter.Fill command into a DataSet.
I've got this code:
NpgsqlCommand n = new NpgsqlCommand();
n.Connection = connector; // a class member NpgsqlConnection
DataSet ds = new DataSet();
DataTable dt = new DataTable();
// DBTablesRef are just constants declared for
// the db table names and columns
ArrayList cols = new ArrayList();
cols.Add(DBTablesRef.all); //all is just *
ArrayList idCol = new ArrayList();
idCol.Add(DBTablesRef.revIssID);
ArrayList idVal = new ArrayList();
idVal.Add(idNum); // a function parameter
// Select builder and Where builder are just small
// functions that return an sql statement based
// on the parameters. n is passed to the where
// builder because the builder uses named
// parameters and sets them in the NpgsqlCommand
// passed in
String select = SelectBuilder(DBTablesRef.revTableName, cols) +
WhereBuilder(n,idCol, idVal);
n.CommandText = select;
try
{
NpgsqlDataAdapter da = new NpgsqlDataAdapter(n);
ds.Reset();
// filling DataSet with result from NpgsqlDataAdapter
da.Fill(ds);
// C# DataSet takes multiple tables, but only the first is used here
dt = ds.Tables[0];
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
So my problem is this: the above code works perfectly, just like I want it to. However, if instead of doing a select on all (*) if I try to name individual columns to return from the query I get the information I asked for, but rather than being split up into seperate entries in the data table I get a string in the first index of the data table that looked something like:
"(0,5,false,Bob Smith,7)"
And the data is correct, I would be expecting 0, then 5, then a boolean, then some text etc. But I would (obviously) prefer it to not be returned as just one big string.
Anyone know why if I do a select on * I get a datatable as expected, but if I do a select on specific columns I get a data table with one entry that is the string of the values I'm asking for?
Ok, I figured it out, it was in the SelectBuilder function. When more than one column was listed in the select statement it was wrapping the columns in ()'s, and apparently this causes either postgreSQL or Npgsql to interpret that as a desire to return a list in string form.
How do you take a couple of data tables and put them in a dataset and relate (that doesn't even sound like correct English) them?
I know how to create datatables.
Here is an example from one of my classes
// create the relationship between Booking and Booking_MNI
DataRelation relBookingMNI;
relBookingMNI = new DataRelation("BookingToBookingMNI",dsBooking.Tables["Booking"].Columns["Record_Id"],dsBooking.Tables["Booking_MNI"].Columns["booking_record_id"]);
dsBooking.Relations.Add(relBookingMNI);
dsBooking is my main dataset that contains 2 tables Booking and Booking_MNI
Where the Record_Id is the primary key and booking_record_id is the foreign key
I changed the code below to match my first example. But I think this is what you are looking for. In our production code this will produce the plus "+" symbol to the left of the row which would allow you to drill into the related table. Again I took production code and made it look like the first example so I don't know if it will compile but it should get you going in the right direction.
DataTable dtBooking = ds.Tables[0];
DataTable dtBooking_MNI = ds.Tables[1];
dtBooking.PrimaryKey = new DataColumn[] {dtBooking.Columns["Record_Id"]};
dtBooking_MNI.PrimaryKey = new DataColumn[] {dtBooking_MNI.Columns["booking_Record_Id"]};
/* Setup DataRelation between the DataTables */
DataColumn[] dcBookingColsArray = new DataColumn[1] {dtBooking.Columns["Record_Id"]};
DataColumn[] dcBookingMNIColsArray = new DataColumn[1] {dtBooking_MNI.Columns["booking_record_Id"]};
DataRelation relBooking_To_MNI = new DataRelation("Booking_To_MNI",dcBookingColsArray,dcBookingMNIColsArray);
ds.Relations.Add(relBooking_To_MNI_Units);
// grid where you want to display the relationship
grdBooking.DataSource = ds;
Look at the DataRelation class. It is what is used in a DataSet to relate two DataTables together.
Let's say you've got your DataTables named "orders" and "orderDetails". You want to create a relationship between them by their OrderNumber columns. We'll assume that orders is the parent and orderDetails is the child. We want to loop through the orders and then print each one's related sub-totals.
DataSet orderData = new DataSet("OrderData");
orderData.Tables.Add(orders);
orderData.Tables.Add(orderDetails);
orderData.Relations.Add("Order_OrderDetails", orders.Columns["OrderNumber"], orderDetails.Columns["OrderNumber"]);
Now, when you want to use that relationship somewhere else in your code:
DataRelation orderRelation = orderData.Relations["Order_OrderDetails"];
foreach (DataRow order in orders.Rows)
{
Console.WriteLine("Subtotals for Order {0}:", order["OrderNumber"]);
foreach (DataRow orderDetail in order.GetChildRows(orderRelation))
{
Console.WriteLine("Order Line {0}: {1}", orderDetail["OrderLineNumber"], string.Format("{0:C}", orderDetail["Price"]));
}
}
try this here is two table 1. categories & 2. Products
string query = "SELECT * FROM Categories; SELECT * FROM Products";
SqlConnection con = new SqlConnection();
SqlDataAdapter da = new SqlDataAdapter(query,con);
DataSet ds = new DataSet();
da.Fill(ds, "CategoriesAndProducts"); //CategoriesAndProducts dataset
string s = ds.Tables[0].Rows[0]["Name"].ToString();
string s1 = ds.Tables[1].Rows[0]["Name"].ToString();
Console.WriteLine(s); //from categories [0][0] like Electronic
Console.WriteLine(s1); //from Products [0][0] like LG
Have you looked into LINQ?
http://msdn.microsoft.com/en-us/netframework/aa904594.aspx
Perhaps you're looking for an orm solution like Entity Framework, NHibernate or Linq to SQL?
Appologies if I've misunderstood the question.
If you use Visual Studio 2005 or later try the following:
Right-click your project and select "Add/NewItem...", then choose DataSet from the wizard, which will create you some xsd and open the dataset designer.
Now you can create multiple tables, add columns to each table and draw relations (foreign key, with/without cascading...) between those tables.
in the autogenerated [YourNewDataSet}.Designer.cs-file, you will find the source code for these relations.
Something like this:
this.relationFK_DataTable2_DataTable1 = new global::System.Data.DataRelation("FK_DataTable2_DataTable1", new global::System.Data.DataColumn[] {
this.tableDataTable2.asdfasColumn}, new global::System.Data.DataColumn[] {
this.tableDataTable1.asdfaColumn}, false);
As always you can strip quite some portion of this code, if you code by hand instead of using the designer.
private void CreateRelation()
{
// Get the DataColumn objects from two DataTable objects
// in a DataSet. Code to get the DataSet not shown here.
DataColumn parentColumn =
DataSet1.Tables["Customers"].Columns["CustID"];
DataColumn childColumn =
DataSet1.Tables["Orders"].Columns["CustID"];
// Create DataRelation.
DataRelation relCustOrder;
relCustOrder = new DataRelation("CustomersOrders",
parentColumn, childColumn);
// Add the relation to the DataSet.
DataSet1.Relations.Add(relCustOrder);
}