C#4.0 : MethodBag & DynamicObject

Read this great article about C#4.0 MethodBag and System.Dynamic.DynamicObject

http://msdn.microsoft.com/en-us/library/ee658247.aspx

Namaste!
Anugrah Atreya

 

LINQ to SQL : Understanding Query Execution

Query Execution

Whether you write a query as a high-level query expression or build one out of the individual operators, the query that you write is not an imperative statement executed immediately. It is a description. For example, in the declaration below the local variable q refers to the description of the query not the result of executing it.

var q =
   from c in db.Customers
   where c.City == "London"
   select c;
foreach (Customer c in q)
   Console.WriteLine(c.CompanyName);

The actual type of q in this instance is IQueryable<Customer>. It's not until the application attempts to enumerate the contents of the query that it actually executes. In this example the foreach statement causes the execution to occur.

An IQueryable object is similar to an ADO.NET command object. Having one in hand does not imply that a query was executed. A command object holds onto a string that describes a query. Likewise, an IQueryable object holds onto a description of a query encoded as a data structure known as an Expression. A command object has an ExecuteReader() method that causes execution, returning results as a DataReader. An IQueryable object has a GetEnumerator() method that causes the execution, returning results as an IEnumerator<Customer>.

Therefore, it follows that if a query is enumerated twice it will be executed twice.

var q =
   from c in db.Customers
   where c.City == "London"
   select c;
// Execute first time
foreach (Customer c in q)
   Console.WriteLine(c.CompanyName);
// Execute second time
foreach (Customer c in q)
   Console.WriteLine(c.CompanyName);

This behavior is known as deferred execution. Just like with an ADO.NET command object it is possible to hold onto a query and re-execute it.

Of course, application writers often need to be very explicit about where and when a query is executed. It would be unexpected if an application were to execute a query multiple times simply because it needed to examine the results more than once. For example, you may want to bind the results of a query to something like a DataGrid. The control may enumerate the results each time it paints on the screen.

To avoid executing multiple times convert the results into any number of standard collection classes. It is easy to convert the results into a list or array using the standard query operators ToList() or ToArray().

var q =
   from c in db.Customers
   where c.City == "London"
   select c;
// Execute once using ToList() or ToArray()
var list = q.ToList();
foreach (Customer c in list)
   Console.WriteLine(c.CompanyName);
foreach (Customer c in list)
   Console.WriteLine(c.CompanyName);

This post is modified version of article "Introduction to LINQ" given at MSDN

Namaste !

Anugrah Atreya

LINQ : CopyToDataTable Where the Generic Type T Is Not a DataRow

Hi All,

Last week I was working on a LINQ2DataSet and LINQ2XML based application. There I happened to use .CopyToDataTable() method.

DataSet ds = new DataSet();

ds.ReadXml("C:\TestXML");

var query = from row in ds.Tables[0].AsEnumerable()

where row.Field<string>("IsActive") == "1"

select new { ID = row.Field<string>("ID"), UserName = row.Field<string>("UserName") };

DataTable dtResults = query.CopyToDataTable();

I got an error something like this:

The type 'AnonymousType#1' cannot be used as type parameter 'T' in the generic type or method 'System.Data.DataTableExtensions.CopyToDataTable<T>(System.Collections.Generic.IEnumerable<T>)'. There is no implicit reference conversion from 'AnonymousType#1' to 'System.Data.DataRow'.

This error will go if you select complete DataRow like this:

DataSet ds = new DataSet();

ds.ReadXml("C:\TestXML");

var query = from row in ds.Tables[0].AsEnumerable()

where row.Field<string>("IsActive") == "1"

select row;

DataTable dtResults = query.CopyToDataTable();

The root cause of this issue is the defination of CopyToDataTable ().

Simply right click on function name and select "GoTo Defination".

public static DataTable CopyToDataTable<T>(this IEnumerable<T> source) where T : DataRow;

You can see that CopyToDataTable<T> is restricted for DataRow by "where T : DataRow" clause.

In case you have to have this working on the purely generic type (i.e.runtime DataRow object) you need to use custom method CopyToDataTable2() for which you need to manually add these extra files to your project as mentioned on these links:

http://msdn.microsoft.com/en-us/library/bb669096.aspx

Namaste !

Anugrah Atreya

Detect and avoid memory leaks in .NET

Sharing this great memory leak article on MSDN (Though I myself have to read it)
http://msdn.microsoft.com/en-us/library/ee658248.aspx

Namaste (Greetings)
| Anugrah Atreya

BULK COPY/INSERT Example !

Hi,

Recently I faced a scenario where I have to copy multiline data in varchar(2000) field from one data base to another database.
I tried copy and paste in SQL Server Management Studio and always eneded up with only top row of multi row data in target table.

Writing an ETL (previously know as DTS) was an expensive approach.
I was testing something so I just copied the data to query editor and wrote an insert query  and managed with duplicate multi-line data in all rows.

Somehow I missed to used BULK COPY and INSERT approach and thus I though to share it below:

exec master..xp_cmdshell 'bcp "Select * from myDB..myTable" queryout "C:\Data.txt" -c -T -t "^,~!@"'

BULK INSERT myDB..myTable FROM 'c:\Data.txt' WITH (FIELDTERMINATOR = '^,~!@')

1 important note here is that you need to enable xp_cmdshell before doing this using your SQL Server Management Studio.

usage: bcp {dbtable | query} {in | out | queryout | format} datafile
[-m maxerrors] [-f formatfile] [-e errfile]
[-F firstrow] [-L lastrow] [-b batchsize]
[-n native type] [-c character type] [-w wide character type]
[-N keep non-text native] [-V file format version] [-q quoted identifier]
[-C code page specifier] [-t field terminator] [-r row terminator]
[-i inputfile] [-o outfile] [-a packetsize]
[-S server name] [-U username] [-P password]
[-T trusted connection] [-v version] [-R regional enable]
[-k keep null values] [-E keep identity values]
[-h "load hints"] [-x generate xml format file]

Namaste (Greetings)

Most useful GPG Commands : you wont find this anywhere else on internet !

I spent more than 2 days to explore these commands on my own. No documentation, no forum, no post will explain below given points:

1. How to use passphrase in batch command ?

gpg -o "C:\Data_Readable.txt" --batch --passphrase-fd 0 < "C:\My_Passphrase.txt" -d "C:\Data_Encrypted.txt"

i.e. Passphrase is stored in a predefined file and its read from there.

 

2. How to use Fingerprint in delete batch command?

You banged your head against the wall and still getting below given error

gpg: key "61ED 3960 36C8 F91A 406B BEA0 4D3C 8843 3D2D 1636" not found: Unknown system error
gpg: 61ED 3960 36C8 F91A 406B BEA0 4D3C 8843 3D2D 1636: delete key failed: Unknown system error

Here is the right BATCH DELETE command:

gpg --batch --yes --delete-secret-and-public-key 61ED396036C8F91A406BBEA04D3C88433D2D1636

i.e. Fingerprint should not contain any spaces in between.

| namaste from Anugrah

Not able to run UnitTest cases when you open your project from shared location ?

Hi All,

I am using Integrated Unit Testing framework of Visual Studio 2008 (i.e. Microsoft.VisualStudio.QualityTools.UnitTestFramework). Recently I faced this issue(in heading/subject) when I opened my project from a dynamic view of clearacse(basically a shared drive)

The actual error which I got was: UTA057: The test 'XXX' cannot be executed because the assembly 'XXX.dll' is not fully trusted by .NET Framework Security Policy. Please use a local directory as the deployment directory for the test run, or use the .NET Framework Configuration tool to grant this assembly the Full Trust permission, and then try again.

The project I was testing is a class library and quick solution for this problem which I got is to uncheck the ENABLE DEPLOYMENT checkbox in LocalTestRun.testrunconfig.

If you don’t want to open this file in VS2008 then you can directly open the file in notepad add following tag <Deployment enabled="false" /> . By default deployment is enabled and the line mentioned above does not exist in this file.

I still need to check that what is the usage of enabling Deployment in this context. If you have used it then do send me comments.

But for now Happy Unit Testing and better development :)

| Anugrah Atreya