WebMatrix 3 - WebGrid and ADO.NET Dataset with DB2 - db2

I'm querying a DB2 server using WebMatrix. I figured it would be easier for quick, proof of concept related tasks... but using DB2 rather than its built-in providers has been challenge, to say the least.
I know my results are coming back since I can iterate thru my dataset just fine and see my results.
I'm trying to use the built-in WebGrid() function within WebMatrix to display my results and keep getting errors:
CS1502: The best overloaded method match for
'System.Web.Helpers.WebGrid.WebGrid(System.Collections.Generic.IEnumerable,
System.Collections.Generic.IEnumerable, string, int, bool,
bool, string, string, string, string, string, string, string)' has
some invalid arguments
My code is basically:
OleDbConnection conn = new OleDbConnection(connString);
DataTable td = new DataTable;
OleDbDataAdapter da = new OleDbDataAdapter("SELECT USER, GROUP FROM DBO.TEST", connString);
ds = new DataSet();
da.Fill(ds);
var results = new WebGrid(ds.Tables[0].Rows);
Of course, its failing on:
var results = new WebGrid(ds.Tables[0].Rows);
Any help or direction would be appreciated. I'm assuming I need to convert this to a System.Collections.Generic.IEnumerable, but no idea how to accomplish this...?

You can't pass a DataTable into a WebGrid. The WebGrid wants an Enumerable that has public properties that it can use as column names. What you can do is to use Linq To DataSet to project the content of the DataTable into a more suitable form. The WebGrid will accept an anonymous type:
OleDbConnection conn = new OleDbConnection(connString);
DataTable td = new DataTable;
string query = #"SELECT USER, GROUP FROM DBO.TEST";
OleDbDataAdapter da = new OleDbDataAdapter(query, connString);
da.Fill(dt);
var data = dt.AsEnumerable().Select(r => new {
User = r.Field<string>("USER"),
Group = r.Field<string>("GROUP")
});
WebGrid results = new WebGrid(data);

Related

How to fix FirstOrDefault returning Null in Linq

My Linq Query keeps returning the null error on FirstOrDefault
The cast to value type 'System.Int32' failed because the materialized value is null
because it can't find any records to match on the ClinicalAssetID form the ClinicalReading Table, fair enough!
But I want the fields in my details page just to appear blank if the table does not have matching entry.
But how can I handle the null issue when using the order by function ?
Current Code:
var ClinicalASSPATINCVM = (from s in db.ClinicalAssets
join cp in db.ClinicalPATs on s.ClinicalAssetID equals cp.ClinicalAssetID into AP
from subASSPAT in AP.DefaultIfEmpty()
join ci in db.ClinicalINSs on s.ClinicalAssetID equals ci.ClinicalAssetID into AI
from subASSINC in AI.DefaultIfEmpty()
join co in db.ClinicalReadings on s.ClinicalAssetID equals co.ClinicalAssetID into AR
let subASSRED = AR.OrderByDescending(subASSRED => subASSRED.MeterReadingDone).FirstOrDefault()
select new ClinicalASSPATINCVM
{
ClinicalAssetID = s.ClinicalAssetID,
AssetTypeName = s.AssetTypeName,
ProductName = s.ProductName,
ModelName = s.ModelName,
SupplierName = s.SupplierName,
ManufacturerName = s.ManufacturerName,
SerialNo = s.SerialNo,
PurchaseDate = s.PurchaseDate,
PoNo = s.PoNo,
Costing = s.Costing,
TeamName = s.TeamName,
StaffName = s.StaffName,
WarrantyEndDate = subASSPAT.WarrantyEndDate,
InspectionDate = subASSPAT.InspectionDate,
InspectionOutcomeResult = subASSPAT.InspectionOutcomeResult,
InspectionDocumnets = subASSPAT.InspectionDocumnets,
LastTypeofInspection = subASSINC.LastTypeofInspection,
NextInspectionDate = subASSINC.NextInspectionDate,
NextInspectionType = subASSINC.NextInspectionType,
MeterReadingDone = subASSRED.MeterReadingDone,
MeterReadingDue = subASSRED.MeterReadingDue,
MeterReading = subASSRED.MeterReading,
MeterUnitsUsed = subASSRED.MeterUnitsUsed,
FilterReplaced = subASSRED.FilterReplaced
}).FirstOrDefault(x => x.ClinicalAssetID == id);
Tried this but doesn't work
.DefaultIfEmpty(new ClinicalASSPATINCVM())
.FirstOrDefault()
Error was:
CS1929 'IOrderedEnumerable<ClinicalReading>' does not contain a definition for 'DefaultIfEmpty' and the best extension method overload 'Queryable.DefaultIfEmpty<ClinicalASSPATINCVM>(IQueryable<ClinicalASSPATINCVM>, ClinicalASSPATINCVM)' requires a receiver of type 'IQueryable<ClinicalASSPATINCVM>'
Feel a little closer with this but still errors
let subASSRED = AR.OrderByDescending(subASSRED => (subASSRED.MeterReadingDone != null) ? subASSRED.MeterReadingDone : String.Empty).FirstOrDefault()
Error:
CS0173 Type of conditional expression cannot be determined because there is no implicit conversion between 'System.DateTime?' and 'string'
The original error means that some of the following properties of the ClinicalASSPATINCVM class - MeterReadingDone, MeterReadingDue, MeterReading, MeterUnitsUsed, or FilterReplaced is of type int.
Remember that subASSRED here
let subASSRED = AR.OrderByDescending(subASSRED => subASSRED.MeterReadingDone).FirstOrDefault()
might be null (no corresponding record).
Now look at this part of the projection:
MeterReadingDone = subASSRED.MeterReadingDone,
MeterReadingDue = subASSRED.MeterReadingDue,
MeterReading = subASSRED.MeterReading,
MeterUnitsUsed = subASSRED.MeterUnitsUsed,
FilterReplaced = subASSRED.FilterReplaced
If that was LINQ to Objects, all these would generate NRE (Null Reference Exception) at runtime. In LINQ to Entities this is converted and executed as SQL. SQL has no issues with expression like subASSRED.SomeProperty because SQL supports NULL naturally even if SomeProperty normally does not allow NULL. So the SQL query executes normally, but now EF must materialize the result into objects, and the C# object property is not nullable, hence the error in question.
To solve it, find the int property(es) and use the following pattern inside query:
SomeIntProperty = (int?)subASSRED.SomeIntProperty ?? 0 // or other meaningful default
or change receiving object property type to int? and leave the original query as is.
Do the same for any non nullable type property, e.g. DateTime, double, decimal, Guid etc.
You're problem is because your DefaultIfEmpty is executed AsQueryable. Perform it AsEnumerable and it will work:
// create the default element only once!
static readonly ClinicalAssPatInVcm defaultElement = new ClinicalAssPatInVcm ();
var result = <my big linq query>
.Where(x => x.ClinicalAssetID == id)
.AsEnumerable()
.DefaultIfEmpty(defaultElement)
.FirstOrDefault();
This won't lead to a performance penalty!
Database management systems are extremely optimized for selecting data. One of the slower parts of a database query is the transport of the selected data to your local process. Hence it is wise to let the DBMS do most of the selecting, and only after you know that you only have the data that you really plan to use, move the data to your local process.
In your case, you need at utmost one element from your DBMS, and if there is nothing, you want to use a default object instead.
AsQueryable will move the selected data to your local process in a smart way, probably per "page" of selected data.
The page size is a good compromise: not too small, so you don't have to ask for the next page too often; not too large, so that you don't transfer much more items than you actually use.
Besides, because of the Where statement you expect at utmost one element anyway. So that a full "page" is fetched is no problem, the page will contain only one element.
After the page is fetched, DefaultIfEmpty checks if the page is empty, and if so, returns a sequence containing the defaultElement. If not, it returns the complete page.
After the DefaultIfEmpty you only take the first element, which is what you want.

Entity Framework Core, Stored Procedure

I am totally confused regarding how to use Stored Procedures using Entity Framework Core. If the stored procedure return an anonymous type, how do I retrieve the data? If the return type is not anonymous, what should I do? How do I add input/output parameters?
I am asking these questions because everywhere I look, I get a different answer. I guess EF Core is evolving rapidly and Microsoft is dabbling with a lot of ideas.
How do I add input/output parameters?
I'm going to answer this particular question of yours.
Below is a TSQL stored procedure with two input and two output parameters
CREATE PROCEDURE [dbo].[yourstoredprocedure]
-- Add the parameters for the stored procedure here
#varone bigint
,#vartwo Date
,#varthree double precision OUTPUT
,#varfour bigint OUTPUT
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
-- YOUR CODE HERE
SET #varthree = 10.02;
SET #varfour = #varone;
return;
END
Now To execute this stored procedure using Entity Framework Core
MyContext.Database
.ExecuteSqlCommand(#"EXECUTE [yourstoredprocedure] " +
" {0} " +
", {1} " +
",#varthree OUTPUT " +
", #varfour OUTPUT ", dataOne, dataTwo, outputVarOne, outputVarTwo);
var outputResultOne= outputVarOne.Value as double?;
var outputResultTwo= outputVarTwo.Value as long?;
You can pass your input simply using parameterized query as above. You can also create named parameters. such as for output parameters, I've created two named parameters as -
var outputVarOne = new SqlParameter
{
ParameterName = "#varthree ",
DbType = System.Data.DbType.Double,
Direction = System.Data.ParameterDirection.Output
};
var outputVarTwo = new SqlParameter
{
ParameterName = "#varfour ",
DbType = System.Data.DbType.Int64,
Direction = System.Data.ParameterDirection.Output
};
And This is how using EF Core you execute a stored procedure with input and output parameters. Hope this helps someone.
This solution provides methods that call a stored procedure and maps the returned value to a defined (non-model) entity. https://github.com/verdie-g/StoredProcedureDotNetCore
Microsoft address this issue:
"SQL queries can only be used to return entity types that are part of your model. There is an enhancement on our backlog to enable returning ad-hoc types from raw SQL queries." https://learn.microsoft.com/en-us/ef/core/querying/raw-sql
And here is the issue tracked in GitHub: https://github.com/aspnet/EntityFramework/issues/1862
you might use an extention like StoredProcedureEFCore
Then the usage is more intuitively.
List rows = null;
ctx.LoadStoredProc("dbo.ListAll")
.AddParam("limit", 300L)
.AddParam("limitOut", out IOutParam<long> limitOut)
.Exec(r => rows = r.ToList<Model>());
long limitOutValue = limitOut.Value;
ctx.LoadStoredProc("dbo.ReturnBoolean")
.AddParam("boolean_to_return", true)
.ReturnValue(out IOutParam<bool> retParam)
.ExecNonQuery();
bool b = retParam.Value;
ctx.LoadStoredProc("dbo.ListAll")
.AddParam("limit", 1L)
.ExecScalar(out long l);

Getting "The SqlParameter is already contained by another SqlParameterCollection." error while using SqlQuery command

I am trying to parameterize a dynamic query and run it using SqlQuery method in Entity Framework code first.
The first time I execute SqlQuery it works as expected so I am sure there is nothing wrong with query or parameters but immediately I execute the same command with the same parameters second time and I get this error
"The SqlParameter is already contained by another SqlParameterCollection."
Since I am already using ToList() method here, I have no idea what the cause could be!
Here is the simulated code.
using (var context = Common.GetDbContext())
{
var parameters = new List<SqlParameter>();
//populating parameters here...
var sqlQuery = "Select * from MyTable where UserId=#p1 and And Active=#p2";
// first time
var result = context.Database.SqlQuery<ResultType>(sqlQuery, parameters.ToArray()).ToList();
//second time
result = context.Database.SqlQuery<ResultType>(sqlQuery, parameters.ToArray()).ToList();
}
Any idea?
Hi SqlParameter is clonable. Try this:
result = context.Database.SqlQuery<ResultType>(sqlQuery, parameters.Select(x => x.Clone()).ToArray()).ToList();
See https://msdn.microsoft.com/en-us/library/vstudio/bb338957%28v=vs.100%29.aspx

iDB2Commands in Visual Studio 2010

These are the basic things I know about iDB2Commands to be used in Visual Studio 2010. Could you please help me how could I extract data from DB2? I know INSERT, DELETE and Record Count. But SELECT or Extract Data and UPDATE I don't know.
Imports IBM.Data.DB2
Imports IBM.Data.DB2.iSeries
Public conn As New iDB2Connection
Public str As String = "Datasource=10.0.1.11;UserID=edith;password=edith;DefaultCollection=impexplib"
Dim cmdUpdate As New iDB2Command
Dim sqlUpdate As String
conn = New iDB2Connection(str)
conn.Open()
'*****Delete Records and working fine
sqlUpdate = "DELETE FROM expusers WHERE username<>#username"
cmdUpdate.Parameters.Add("username", iDB2DbType.iDB2Date)
cmdUpdate.Parameters("username").Value = ""
'*****Insert Records and working fine
sqlUpdate = "INSERT INTO expusers (username, password, fullname) VALUES (#username, #password, #fullname)"
cmdUpdate.Parameters.Add("username", iDB2DbType.iDB2VarChar)
cmdUpdate.Parameters.Add("password", iDB2DbType.iDB2VarChar)
cmdUpdate.Parameters.Add("fullname", iDB2DbType.iDB2VarChar)
cmdUpdate.Parameters("username").Value = txtUsername.Text
cmdUpdate.Parameters("password").Value = txtPassword.Text
cmdUpdate.Parameters("fullname").Value = "Editha D. Gacusana"
'*****Count Total Records and working fine
Dim sqlCount As String
Dim cmd As New iDB2Command
sqlCount = "SELECT COUNT(*) AS count FROM import"
cmd = New iDB2Command(Sql, conn)
Dim count As Integer
count = Convert.ToInt32(cmd.ExecuteScalar)
'*****Update Records and IT IS NOT WORKING AT ALL
sqlUpdate = "UPDATE expusers SET password = #password WHERE RECNO = #recno"
cmdUpdate.Parameters.Add("recno", iDB2DbType.iDB2Integer)
cmdUpdate.Parameters.Add("password", iDB2DbType.iDB2VarChar)
cmdUpdate.Parameters("recno").Value = 61
cmdUpdate.Parameters("password").Value = txtPassword.Text
cmdUpdate.Connection = conn
cmdUpdate.CommandText = sqlUpdate
cmdUpdate.ExecuteNonQuery()
conn.Close()
Please help me how to code the SELECT query wherein I could extract/fetch data from DB2 Database. Also, how could i update the records in the database.
Thanks!
Instead of ExecuteNonQuery(), look at ExecuteReader(). I don't have VS2010 installed, but try something like this:
iDB2Command cmdSelect = new iDB2Command("SELECT username, password, fullname FROM expusers", conn);
cmdSelect.CommandTimeout = 0;
iDB2DataAdapter da = new iDB2DataAdapter(cmdSelect);
DataSet ds = new DataSet();
da.Fill(ds, "item_master");
GridView1.DataSource = ds.Tables["expusers"];
GridView1.DataBind();
Session["TaskTable"] = ds.Tables["expusers"];
da.Dispose();
cmdSelect.Dispose();
cn.Close();
See: http://gugiaji.wordpress.com/2011/12/29/connect-asp-net-to-db2-udb-for-iseries/
If you aren't trying to bind to a grid, look at iDB2Command.ExecuteReader() and iDB2DataReader()
The DELETE is working fine? The code has the parameter type for "username" set to iDB2Date. The INSERT has "username" set to iDB2VarChar. How is the column defined in the table? Char, Varchar or Date?
On the UPDATE, you reference RECNO, but that does not seem to be a column in the table. Updating a relational database table by row number is a bad idea - the row numbers are not guaranteed to stay constant. If you are just testing, as I think you are, don't use RECNO, use RRN(). The DB2 for i syntax is WHERE rrn(expusers) = #recno
To help your testing, do a SELECT without a WHERE clause and list out all the rows. Make sure the name stored in the username column matches the name you are trying to update. Pay particular attention to the case of the data. If the name in expusers looks like "EDITHA D. GACUSANA", and #username is "Editha D. Gacusana" then it will not match on the WHERE clause.

split values of couch db result

I want to split the values selected from couch db in gwt according to a particular id. I tried to use the String tokenizer but couldn't found something useful. the result returned from couch db is in the following format:
{"_id":"2","_rev":"1-717f76046030a683687ace9ac8f7bdbf","course":"jbdgjbj","passwd":"rty","phone":"24125514444","clgnme":"bjfbjf","address":"jbjfbjb","name":"meenal","cpasswd":"rty","user":"2","fname":"jfbg"}
I just want to get the values and set them in textboxes.
how to do it?
try this ...
Session studentDbSession = new Session("localhost",5984);
Database studentCouchDb = studentDbSession.getDatabase("student");
System.out.println("select");
Document d = studentCouchDb.getDocument(input);
if(d.containsKey("FirstName")){
fname=d.getString("FirstName");//fname is variable
}
if(d.containsKey("LastName")){
lname=d.getString("LastName");//lname is variable
}
if(d.containsKey("Address")){
add= d.getString("Address");//add name is variable
}
finally concatenate all strings and return to client...
all=fname+" "+lname+" "+add;
return all;
This looks like JSON. You can parse it using JSONObject:
JSONObject obj = new JSONObject(yourString);
String course = obj.getString("course");