New LinqPad user help.

ddecoste

I have started looking into LinqPad to help me with my LINQ querys in vb.net programs. What I would like to do is export my xml dataset then use that in LinqPad. I have exported my dataset but I have been having trouble setting the XML as a datasource and running a simple query against it. When I use the code in the FAQ I get an error saying Object reference not set to an instance of an object. It is probably since I have multiply tables in this xml and I am not sure how to specify the table. I am attaching a screen capture of the XML datasource with 4 tables in it and I have expanded one table showing the columns. Any help to get me started would be great. Here is the code I have:

var xml = XElement.Load (@c:\\TEMP\MyData.xml);

var query =
from e in xml.Elements()
where e.Attribute ("LocNum").Value == "Something"
select e;

query.Dump();




Please remember I would like to work in VB.net.

A valid table name is "tbl_MsView_Items"




Thank you for all the help.

nescafe

Your screenshot is missing.

However the code works.

When supplying the correct input.

C#:

var xml = XElement.Load(@"c:\TEMP\MyData.xml");

var query =
  from e in xml.Elements()
  where e.Attribute("LocNum").Value == "Something"
  select e;

query.Dump();

Input:

<Locations>
  <Location LocNum="Something"/>
</Locations>

Output:

IEnumerable (1 item)
<Location LocNum="Something" />

When supplying incorrect input:

<Locations>
  <Location />
</Locations>

.., the code fails (note that the incorrect line is highlighted) on the following line:

  where e.Attribute("LocNum").Value == "Something"

Because the attribute LocNum is absent.

You can fix this by replacing the above line with these:

  let locNum = e.Attribute("LocNum")
  where locNum != null && locNum.Value == "Something"

This will check for an existing attribute before checking its value.

Or the LINQPad 5 method:

  where e.Attribute("LocNum")?.Value == "Something"

If you'd like to code in VB.Net then you should supply an example in VB.Net Or run the code through an converter: http://converter.telerik.com/

ddecoste

nescafe,

Thank you. I am a total newb to this. The only reason I was using the C# statements was that was all that was in the FAQ. I did run it through the converter to this. Thank you for that link to the converter.


Dim xml = XElement.Load("c:\\TEMP\MyData.xml")

Dim query = From e In xml.Elements() Where e.Attribute("LocNum").Value = "Someplace"

query.Dump()


Since the screen shot of the data did not come through. I will paste the some raw data instead. This XML has 4 tables in it, below is just one.

Snippet of the xml Schema









....

Snippet of the data

Cust1
Someplace
Somegroup
1030928
abcdef
60.01

Once again thank you for your patience. I am really looking to just get started with a simple query to pull back records.

nescafe

How about applying the mentioned fix first and then running it through the converter?

(Also, the data you posted is missing the necessary xml markup)

Edit: It's great to start with "a simple query" (we've all started with simple examples), but you have to understand what the error means and how to solve it.

The error is: "Object reference not set to an instance of an object." and the cursor points to the equation: where e.Attribute("LocNum").Value == "Something". This means that somewhere in this equation, a reference to an object is missing. Most likely, there is a tag without an attribute LocNum for which no property Value can be read.

I have given a solution for this, so it's up to you to give it a try and show what happens next.

ddecoste

nescafe

Once again thank you.

Yes I did try the fix and it works and nothing is returned, no errors I think that the issue is referencing the correct tags in the XML. I do not know the correct term for this in pertaining to XML, but the XML has 4 tables. In the past in linq I reference the table like this in vb.net

Dim query = From H In dataset.Tables("SomeTable").AsEnumerable() _ Where H.Field(Of String)("SomeColumn").Equals (SomeString) _

I am not sure how to do this referencing the table then the column in XML. I know the statement is not returning anything since the "LocNum" is actually a sub-child element.

I was hoping to just post a little snippet of the XML but the actual XML did not make it.
Here is the XML and one data row

<?xml version="1.0" standalone="yes"?> <ProgramData> <xs:schema id="ProgramData" xmlns="" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata"> <xs:element name="ProgramData" msdata:IsDataSet="true" msdata:UseCurrentLocale="true"> <xs:complexType> <xs:choice minOccurs="0" maxOccurs="unbounded"> <xs:element name="tbl_OpenOrdersSummary"> <xs:complexType> <xs:sequence> <xs:element name="ord_no" type="xs:string" minOccurs="0" /> <xs:element name="cus_no" type="xs:string" minOccurs="0" /> <xs:element name="cus_alt_adr_cd" type="xs:string" minOccurs="0" /> <xs:element name="ord_type" type="xs:string" minOccurs="0" /> <xs:element name="Ord_Type_Desc" type="xs:string" minOccurs="0" /> </xs:sequence> </xs:complexType> </xs:element> <xs:element name="tbl_MsView_Items"> <xs:complexType> <xs:sequence> <xs:element name="CustNum" type="xs:string" minOccurs="0" /> <xs:element name="LocNum" type="xs:string" minOccurs="0" /> <xs:element name="CustGroup" type="xs:string" minOccurs="0" /> <xs:element name="ItemCode" type="xs:string" minOccurs="0" /> <xs:element name="ItemDesc" type="xs:string" minOccurs="0" /> <xs:element name="ItemOrder" type="xs:string" minOccurs="0" /> <xs:element name="CustPartNum" type="xs:string" minOccurs="0" /> <xs:element name="DirectShip" type="xs:string" minOccurs="0" /> <xs:element name="Consign" type="xs:string" minOccurs="0" /> </xs:sequence> </xs:complexType> </xs:element> </xs:choice> </xs:complexType> </xs:element> </xs:schema> <tbl_MsView_Items> <CustNum>SomeCust</CustNum> <LocNum>SomeLoc</LocNum> <CustGroup>SomeGroup</CustGroup> <ItemCode>12198604</ItemCode> <ItemDesc>Description</ItemDesc> <ItemOrder>60.01</ItemOrder> <CustPartNum>abc123</CustPartNum> <DirectShip>No</DirectShip> <Consign>No</Consign> </tbl_MsView_Items> </ProgramData>

nescafe

Why wouldn't you do this using the dataset way?

DataSet:

Dim ds = New DataSet()
ds.ReadXml("C:\Temp\MyData.xml")

Dim table = ds.Tables("tbl_MsView_Items")

Dim query =
  From r In table.AsEnumerable()
  Where r.Field(Of String)("LocNum") = "SomeLoc"
  Select r

query.Dump()

Otherwise, LINQ to XML:

Dim xml = XDocument.Load("C:\Temp\MyData.xml")

Dim query =
  From e In xml.Element("ProgramData").Elements("tbl_MsView_Items")
  Where e.Element("LocNum").Value = "SomeLoc"
  Select e

query.Dump()

ddecoste

nescafe,

Thank you. Now that works. I guess I did not know I could do it as a Dataset, My thinking was that I did not have access to the dataset to test like this. I was just thinking XML. I have worked so little LINQ I was hoping to use this tool to write and test LINQ queries outside of Visual Studio. By using XML I can get a snapshot of what my data looks like at that point in the program. If I can design it in Dataset format it makes it easier to slap back in the program.

This gives me a good place to start. I was really hoping this would work. I have no problem buying the full product but I just wanted to at least see if I could use it. I looks like we can definately use it.

I will continue to work with this some more, Seeing as I can work directly like it is a dataset, it will make life easier.

Thank you for your help.