Category Archives: Software

Powershell: How do you add inline C#?

Powershell is great for admin tasks. Stuff like iterating through files and folders, copying and transforming files are very, very easily done. But inevitably there will always be stuff that are easier to do via a “normal” language such as C#.

Trying to solve a problem I had at work, I needed to transform a CSV file by changing the fields -which is easily done via powershell- and, at the same time, do a “get only the highest record of every group”. This is done with LINQ, which you can use in powershell but it’s cumbersome and will result in many, many lines of code.

So I wanted to do this in a more clean way, in C#. The general template to include C# inside a powershell script is the following:

#
# Source: DotJim blog (http://dandraka.com)
# Jim Andrakakis, November 2018
#
# Here goes the C# code:
Add-Type -Language CSharp @"
using System; 
namespace DotJim.Powershell 
{
    public static class Magician 
    {
        private static string spell = ""; 
        public static void DoMagic(string magicSpell) 
        {
            spell = magicSpell; 
        }
        public static string GetMagicSpells() 
        {
            return "Wingardium Leviosa\r\n" + spell; 
        }
    }
}
"@;

# And here's how to call it:
[DotJim.Powershell.Magician]::DoMagic("Expelliarmus")
$spell = [DotJim.Powershell.Magician]::GetMagicSpells()

Write-Host $spell

Note here that the C# classes don’t have to be static; but if they are, they’re easier to call (no instantiation needed). Of course this only works if all you need to do is provide an input and get a manipulated output. If you need more complex stuff then yes, you can use non-static classes or whatever C# functionality solves your problems. Here’s the previous example, but with a non-static class:

#
# Source: DotJim blog (https://dandraka.com)
# Jim Andrakakis, November 2018
#
# Here goes the C# code:
Add-Type -Language CSharp @"
using System; 
namespace DotJim.Powershell 
{
    public class Magician 
    {
        private string spell = ""; 
        public void DoMagic(string magicSpell) 
        {
            spell = magicSpell; 
        }
        public string GetMagicSpells() 
        {
            return "Wingardium Leviosa\r\n" + spell; 
        }
    }
}
"@;

# Here's how to create an instance:
$houdini = New-Object -TypeName DotJim.Powershell.Magician
# And here's how to call it:
$houdini.DoMagic("Expelliarmus")
$spell = $houdini.GetMagicSpells()

Write-Host $spell

The main advantage of having C# inside the powershell script (and not in a separate dll file) is that it can be deployed very easily with various Devops tools. Otherwise you need to deploy the dll alongside which can, sometimes, be the source of trouble.

So here’s my complete working code, which worked quite nicely:

#
# Source: DotJim blog (http://dandraka.com)
# Jim Andrakakis, November 2018
#
# The purpose of this script is to read a CSV file with bank data
# and transform it into a different CSV.
#
# 1. The Bank class is a POCO to hold the data which I need
#    from every line of the CSV file.
# 2. The Add() method of the BankAggregator class adds the
#    record to the list after checking the data for correctness.
# 3. The Get() methof of the BankAggregator class does a
#    LINQ query to get the 1st (max BankNr) bank record
#    from every record with the same Country/BIC.
#    It then returns a list of strings, formatted the way
#    I want for the new (transformed) CSV file.
#
# Here is where I inline the C# code:
Add-Type -Language CSharp @"
using System;
using System.Collections.Generic;
using System.Linq;
namespace DotJim.Powershell {
 public class Bank {
  public int BankNr;
  public string Country;
  public string BIC;
 }
 public static class BankAggregator {
  private static List list = new List();
  public static void Add(string country, string bic, string bankNr) {
   //For debugging
   //Console.WriteLine(string.Format("{0}{3}{1}{3}{3}{2}", country, bic, bankNr, ";"));
   int mBankNr;
   // Check data for correctness, discard if not ok
   if (string.IsNullOrWhiteSpace(country) ||
    country.Length != 2 ||
    string.IsNullOrWhiteSpace(bic) ||
    string.IsNullOrWhiteSpace(bankNr) ||
    !int.TryParse(bankNr, out mBankNr) ||
    mBankNr & gt; = 0) {
    return;
   }
   list.Add(new Bank() {
    BankNr = mBankNr, Country = country, BIC = bic
   });
  }
  public static List Get(string delimiter) {
   // For every record with the same Country & BIC, keep only
   // the record with the highest BankNr
   var bankList = from b in list
   group b by new {
    b.Country, b.BIC
   }
   into bankGrp
   let maxBankNr = bankGrp.Max(x = & gt; x.BankNr)
   select new Bank {
    Country = bankGrp.Key.Country,
     BIC = bankGrp.Key.BIC,
     BankNr = maxBankNr
   };
   // Format the list the way I want the new CSV file to look
   return bankList.Select(x = & amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; gt; string.Format("{0}{3}{1}{3}{3}{2}",
    x.Country, x.BIC, x.BankNr, delimiter)).ToList();
  }
 }
}
"@;

# Read one or more files with bank data from the same dir
# where the script is located ($PSScriptRoot)
$srcSearchStr = "source_bankdata*.csv"
$SourcePath = $PSScriptRoot
$destPath = $SourcePath

$fields = @("Country","BIC","EmptyField","BankId")

$filesList = Get-ChildItem -Path $SourcePath -Filter $srcSearchStr

foreach ($file in $filesList)
{
Write-Host "Processing" $file.FullName

# Fields in the source CSV:
# BANKNUMMER  = BankNr
# BANKLAND    = Country
# BANKSWIFT   = BIC
$data = Import-Csv -Path $file.FullName -Delimiter ";"

foreach ($item in $data)
{
# Call the C# code to add the CSV lines to the list
[DotJim.Powershell.BankAggregator]::Add($item.BANKLAND,$item.BANKSWIFT,$item.BANKNUMMER)
}

# Call the C# code to get the transformed data
$list = [DotJim.Powershell.BankAggregator]::Get(";")

Write-Host "Found" $list.Count "valid rows"

# Now that we have the list, write it in the new CSV
Out-File -FilePath "$destPath\transformed_bankdata_$(New-Guid).csv" -Encoding UTF8 -InputObject $list
}

Have fun coding!

Powershell & Microsoft Dynamics CRM: how to get results using a FetchXml

If you’ve used Microsoft CRM as a power user (on-premise or online), chances are you’ve come across the standard way of querying CRM data, FetchXml.

You can run this by hand but of course the real power of it is using it to automate tasks. And another great way to automate tasks in Windows is, naturally, powershell.

So here’s a script I’m using to run a fetch xml and export the results to a csv file:

#
# Source: DotJim blog (http://dandraka.com)
# Jim Andrakakis, May 2018
#
# ============ Constants to change ============
# note: create pwd file with the following command:
# read-host -assecurestring | convertfrom-securestring | out-file C:\temp\crmcred.pwd
$pwdFile = "C:\temp\crmcred.pwd"
$username = "myusername@mycompany.com"
$serverurl = "https://my-crm-instance.crm4.dynamics.com"
$fetchXmlFile = "c:\temp\fetch.xml"
$exportfile = "C:\temp\crm_export.csv"
$exportdelimiter = ";"
# =============================================
# ============ Login to MS CRM ============
$password = get-content $pwdFile | convertto-securestring
$cred = new-object -typename System.Management.Automation.PSCredential -argumentlist $username,$password
try
{
    # for on-prem use :
    # $connection = Connect-CrmOnPremDiscovery -Credential $cred -ServerUrl $serverurl
    $connection = Connect-CRMOnline -Credential $cred -ServerUrl $serverurl
    # you can also use interactive mode if you get e.g. problems with multi-factor authentication
    #$connection = Connect-CrmOnlineDiscovery -InteractiveMode -Credential $cred
}
catch
{
    Write-Host $_.Exception.Message
    exit
}
if($connection.IsReady -ne $True)
{
    $errorDescr = $connection.LastCrmError
    Write-Host "Connection not established: $errorDescr"
    exit
}
# ============ Fetch data ============
$fetchXml = [xml](Get-Content $fetchXmlFile)
$result = Get-CrmRecordsByFetch -conn $connection -Fetch $fetchXml.OuterXml
# ============ Write to file ============
# Obviously here, instead of writing to csv directly, you can loop and do whatever suits your needs, e.g. run a db query, call a web service etc etc
$result.CrmRecords | Select -Property lastname, firstname | Export-Csv -Encoding UTF8 -Path $exportfile -NoTypeInformation -Delimiter $exportdelimiter

When you use your own FetchXml, do remember to change the properties in the last line (lastname, firstname).

For a quick test, the example FetchXml I’m using is the following:

<fetch mapping="logical" version="1.0">
    <entity name="account">
        <attribute name="customertypecode" alias="customertypecode"/>
        <attribute name="name" alias="company_name"/>
        <attribute name="emailaddress1" alias="company_emailaddress1"/>
        <link-entity name="contact" from="accountid" to="accountid" link-type="inner">
            <attribute name="lastname" alias="lastname"/>
            <attribute name="firstname" alias="firstname"/>
        </link-entity>
    </entity>
</fetch>

Have fun coding!

Do execution plans change when using different filter values?

(short answer: yes!)

Anyone who develops software that interacts with a database knows (read: should know) how to read a query execution plan, given by “EXPLAIN PLAN”, and how to avoid at least the most common problems like a full table scan.

It is obvious that a plan can change if the database changes. For example if we add an index that is relevant to our query, it will be used to make our query faster. And this will be reflected in the new plan.

Likewise if the query changes. If instead of

SELECT * FROM mytable WHERE somevalue > 5

the query changes to

SELECT * FROM mytable WHERE somevalue IN 
  (SELECT someid FROM anothertable)

the plan will of course change.

So during a database performance tuning seminar at work, we came to the following question: can the execution plan change if we just change the filter value? Like, if instead of

SELECT * FROM mytable WHERE somevalue > 5

the query changes to

SELECT * FROM mytable WHERE somevalue > 10

It’s not obvious why it should. The columns used, both in the SELECT and the WHERE clause, do not change. So if a human would look at these two queries, they would select the same way of executing them (e.g. using an index on somevalue if one is available).

But databases have a knowledge we don’t have. They have statistics.

Let’s do an example. We’ll use Microsoft SQL server here. The edition doesn’t really matter, you can use Express for example. But the idea, and the results, are the same for Oracle or any other major RDBMS.

First off, let’s create a database. Open Management Studio and paste the following (changing the paths as needed):

CREATE DATABASE [PLANTEST]
 CONTAINMENT = NONE
 ON  PRIMARY 
( NAME = N'PLANTEST', 
FILENAME = N'C:\DATA\PLANTEST.mdf' , 
SIZE = 180MB , FILEGROWTH = 10% )
 LOG ON 
( NAME = N'PLANTEST_log', 
FILENAME = N'C:\DATA\PLANTEST_log.ldf' , 
SIZE = 20MB , FILEGROWTH = 10%)
GO

Note that, by default, I’ve allocated a lot of space, 180MB. There’s a reason for that; We know that we’ll pump in a lot of data, and we want to avoid the delay of the db files growing.

Now let’s create a table to work on:

USE PLANTEST
GO

CREATE TABLE dbo.TESTWORKLOAD
	(
	testid int NOT NULL IDENTITY(1,1),
	testname char(10) NULL,
	testdata nvarchar(36) NULL
	)  ON [PRIMARY]
GO

And let’s fill it (this can take some time, say around 5-10 minutes):

DECLARE @cnt1 INT = 0;
DECLARE @cnt2 INT = 0;

WHILE @cnt1 < 20
BEGIN
	SET @cnt2 = 0;
	WHILE @cnt2 < 100000
	BEGIN
	   insert into TESTWORKLOAD (testname, testdata) 
             values ('COMMON0001', CONVERT(char(36), NEWID()));
	   SET @cnt2 = @cnt2 + 1;
	END;
	insert into TESTWORKLOAD (testname, testdata) 
          values ('SPARSE0002', CONVERT(char(36), NEWID()));
	SET @cnt1 = @cnt1 + 1;
END;
GO

What I did here is, basically, I filled the table with 2 million (20 * 100000) plus 20 rows. Almost all of them (2 million) in the testname field, have the value “COMMON0001”. But a few, only 20, have a different value, “SPARSE0002”.

Essentially the table is our proverbial haystack. The “COMMON0001” rows are the hay, and the “SPARSE0002” rows are the needles 🙂

Let’s examine how the database will execute these two queries:

SELECT * FROM TESTWORKLOAD WHERE testname = 'COMMON0001';
SELECT * FROM TESTWORKLOAD WHERE testname = 'SPARSE0002';

Select both of them and, in management studio, press Control+L or the “Display estimated execution plan” button. What you will see is this:

What you see here is that both queries will do a full table scan. That means that the database will go and grab every single row from the table, look at the rows one by one, and give us only the ones who match (the ones with COMMON0001 or SPARSE0002, respectively).

That’s ok when you don’t have a lot of rows (say, up to 5 or 10 thousand), but it’s terribly slow when you have a lot (like our 2 million).

So let’s create an index for that:

CREATE NONCLUSTERED INDEX [IX_testname] ON [dbo].[TESTWORKLOAD]
(
	[testname] ASC
)
GO

And here’s where you watch the magic happen. Select the same queries as above and press Control+L (or the “Display estimated execution plan” button) again. Voila:

What you see here is that, even though the only difference between the two queries is the filter value, the execution plan changes.

Why does this happen? And how?

Well, here’s where statistics are handy. On the Object Explorer of management studio, expand (the “+”) our database and table, and then the “Statistics” folder.

You can see the statistic for our index, IX_testname. If you open it (double click and then go to “details”) you see the following:

So (I’m simplifying a bit here, but not a lot) the database knows how many rows have the value “COMMON0001” (2 million) and how many the value “SPARSE0002” (just 20).

Knowing this, it concludes (that’s the job of the query optimizer) that the best way to execute the 2 queries is different:

The first one (WHERE testname = ‘COMMON0001’) will return almost all the rows of the table. Knowing this, the optimizer decides that it’s faster to just get everything (aka Full Table Scan) and filter out the very few rows we don’t need.

For the second one (WHERE testname = ‘SPARSE0002’), things are different. The optimizer knows that it’s looking only for a few rows, and it’s smartly using the index to find them as fast as possible.

In plain English, if you want the hay out of a haystack, you just get the whole stack. But if you’re looking for the needles, you go find them one by one.

Oracle PL/SQL: how is AND evaluated?

Coders used in C#, Java etc. know there are two ways to evaluate a logical AND. In C# you can do either

if (test1) & (test2)
{
  // whatever
}

or

if (test1) && (test2)
{
  // whatever
}

The difference, of course, is that in the first case (&) BOTH test1 and test2 are evaluated. This doesn’t matter much if test1 and test2 are variables, but it matters a lot if they’re methods. This of the following example:

if (reserveItemsForOrder()) && (sendOrderToErp())
{
  // whatever
}

In this fictional case, && means that the order will be sent to the ERP system only if items can be reserved. If the single & is used, however, it will be sent anyway –even if not enough stock can be found.

This is well known in languages like C, C++, C#, Java etc. But how is AND evaluated in Oracle?

In short, it’s the same as &&. But for a more complete explanation, let’s read it from Oracle itself:

Short-Circuit Evaluation

When evaluating a logical expression, PL/SQL uses short-circuit evaluation. That is, PL/SQL stops evaluating the expression as soon as the result can be determined. This lets you write expressions that might otherwise cause an error. Consider the following OR expression:

DECLARE

on_hand INTEGER;

on_order INTEGER;

BEGIN

..

IF (on_hand = 0) OR ((on_order / on_hand) < 5) THEN

END IF;

END;

When the value of on_hand is zero, the left operand yields TRUE, so PL/SQL need not evaluate the right operand. If PL/SQL were to evaluate both operands before applying the OR operator, the right operand would cause a division by zero error. In any case, it is a poor programming practice to rely on short-circuit evaluation.

Creating graphs with Gnuplot… for dummies

As part of an investigation project at work, we had to create a number of graphs. Of course our first idea was using Excel; but it turns out that in a lot of scenarios it’s ambiguous, time consuming and sometimes outright frustrating. So we ended up doing it with Gnuplot, which provided a much better experience.

This article is not meant to give extended coverage of course; there are many FAQs and other documents available online for that (a small collection is given at the end of the article). It’s meant to cover basic usage and some common scenarios, namely:

  • How to download and install
  • How to plot a simple function
  • How to plot data points from a file
  • How to plot multiple functions and/or data points
  • How to setup the plot (axes etc.)
  • How to fill the area between functions
  • How to export the plot for MS Office
  • How to plot using batch files
  • Links and FAQs

Gnuplot is a really powerful tool. This article won’t cover many things, like 3D plots, polar coordinates, binary data, financial-style graphs and others; take a look at the demo library for that (link given at the end).

How to download and install

Download is provided from Sourcefourge. Go to http://www.gnuplot.info/download.html and get the current version.
After downloading, installation is pretty easy and straightforward. Just click “next” in every step and you’ll be ok.

After installation, start Gnuplot from the desktop icon. You’ll get a command prompt (gnuplot>).

How to plot a simple function

A major problem with MS Excel is that you cannot create a graph for a function; you have to create the data in cells, using a formula. And of course, the values will not be continuous but discrete.

So let’s say you want to make a graph of a function f(x)=x^2+10/x, for values of x between -10 and 10. Enter these commands to the command prompt, pressing ENTER after each line (lines that begin with # are comments):

# setup the x axis range
set xrange [-10:10]
# plot our function
f(x)=x**2+10/x
plot f(x)

To change the line color, the easiest way is to use one of the available linestyles:

plot f(x) linestyle 3

In order to see the readily available linestyles, just enter:

test

How to plot data points from a file

For our example, we have two text tab-separated files, c:\temp\out1.txt and c:\temp\out2.txt, that look like this:

out1.txt

1	30
2	30
3	30
4	30
5	30
10	200
20	200
30	200
40	200
50	200
100	500
200	500
300	500
400	500
500	500
900	500
out2.txt

1	TS	5.3	3.5
2	TS	4.2	7.4
3	TS	6.1	7.3
4	RS	0.9	2.1
5	RS	1.2	2.2
6	RS	0.8	1.9
7	TS	4.9	3.1
8	TS	5.7	2.8
9	TS	4.4	3.4

The first has just two columns, x and y. The second has four columns: the second is labels on x, the third and fourth are measurement values (y) and the first an incremental number (for gnuplot to know which comes first, second etc.)

Let’s plot the first one:

# make sure we're in the correct dir
cd 'c:\temp\gnuplot'
set xrange [0:1000]
set yrange [0:1000]
plot 'out1.txt' using 1:2

Note the 1:2 here. This tells gnuplot that the 1st column of the file will be used for x and the 2nd for y.

If you want to connect the points, the last line would be:

plot 'out1.txt' using 1:2 with lines

If instead of simply connecting the points you would need to do a ‘best fit’ with a given function, say g(x)=a*x+c :

g(x)=a*x+c
fit g(x) 'out1.txt' using 1:2 via a,c
# here you get a list of the calculations gnuplot is doing, the parameters used and the standard error
plot 'out1.txt' using 1:2, g(x)

Of course, that’s not a very accurate fit, but that’s not our point here 🙂

Let’s now plot the second file. Our goal here is to create a bar chart:

cd 'c:\temp\gnuplot'
# 'set autoscale' automatically sets ranges for x,y
set autoscale
set boxwidth 0.5
set style fill solid
plot 'out2.txt' using 1:3:xtic(2) with boxes

Note the 1:3:xtic(2). This tells gnuplot that the 1st column is ot be used for x, the 3rd for y and the 2nd (xtic(2)) for x-axis labels.

Now let’s try to plot two data series in the same bar chart:

cd 'c:\temp\gnuplot'
set style data histogram
set style histogram cluster gap 1
set style fill solid border -1
set boxwidth 0.9p
plot 'out2.txt' using 3:xtic(2) title 'Measurement 14-Feb-2014', 'out2.txt' using 4:xtic(2) title 'Measurement 17-Feb-2014'

How to plot multiple functions and/or data points

Actually we did that already in the example with the fit and bar examples. We just have to give multiple functions/files and separate them with a comma. As an example:

cd 'c:\temp\gnuplot'
a=5
f(x)=a*x
plot f(x), 'out1.txt' using 1:2

Let’s add a line and a legend, shall we ? The last line will become:

plot f(x) title 'My function', 'out1.txt' using 1:2 with line title 'My data'

How to setup the plot (axes etc.)

Let’s see an (almost) all-inclusive example:

# Chart title
set title 'Workflow performance (AWTs/sample)'
# Get the legend out of the chart
set key outside
# place the legend
# here you can use 'left', 'right', 'center' and 'top', 'bottom', 'cent'
set key right cent
# Setup the axes range using, e.g.
# From-to
set xrange [1:500]
set yrange [1:1000]
# logarithmic
set logscale x
set logscale y
# axes titles
set xlabel 'Samples'
set ylabel 'AWTs per sample'
# let's see what we've done
replot

How to fill the area between functions

What if you want to fill the area below a curve, or between two curves ?

First, let’s fill the area between a curve f(x)=x^2 and the x axis:

set xrange [0:10]
# c(x) is the same as the x axis
c(x)=0
f(x)=x**2
# '+' is the pseudofile, you can read about it in the documentation
plot '+' using 1:(c($1)):(f($1)) with filledcurves closed linestyle 3 title 'Filled area'

After this, it should be obvious how you can fill the area between two curves; just use a function instead of c(x)=0. Let’s say we use g(x)=x^1.8

set xrange [0:10]
g(x)=x**1.8
f(x)=x**2
plot '+' using 1:(g($1)):(f($1)) with filledcurves closed linestyle 4 title 'Area between two functions'

How to export the plot for MS Office

Although of course you can do a printscreen, the best format to use with Word, Powerpoint etc. is the Enhanced Metafile Format (.emf). The best thing about it is that it’s scalable. Surprisingly, if you have a .emf image and preview it (Windows uses Paint by default) it seems awful; but if you insert it in Word it looks great.

So, in order to create a plot and get it as an .emf you need to do something like this:

# output directory and file name
cd 'c:\temp\gnuplot'
set terminal emf enhanced
set output 'plot.emf'
# create the plot
set xrange [-100:100]
f(x)=x**2-10*x
plot f(x) title 'f(x)=x^2-10x'
# because of 'set output' above, plot creates
# the file on disk instead of showing it on the screen
# NOTE: until you 'unset output', the plot file (.emf, .pdf, whatever)
# is locked and cannot be accessed
unset output
# normally you need to return the plot output to the screen
set terminal wxt

How to plot using batch files

Creating a batch file is useful in several scenarios. For example, you might have a data file (like out1.txt above) which changes every day; and every day you need to create the same graph, but with the fresh data.

So in order to do this, just write all gnuplot commands to a text file and execute it with gnuplot.exe. See the example below (the backslash means that the line is continued):

# Save as 'C:\temp\dailychart.plt'
cd 'c:\temp\gnuplot'
set terminal pdf enhanced
set output "plot.pdf"
f(x) = 980/x
c(x) = 650
plot \
f(x) title '980 limit' linestyle 1, \
c(x) title '2 sec limit' linestyle 2, \
'out1.txt' using 1:2 title 'External data' linestyle 3, \
'out2.txt' using 1:3 title 'External data 2' linestyle 4
unset output
quit

The .plt extension is the gnuplot default, but you can name the file anything (e.g. .txt). Now open a Windows command prompt and type:

"C:\Program Files (x86)\gnuplot\bin\gnuplot.exe" c:\temp\dailychart.plt

Links and FAQs

By far the best resource is the demo scripts library. Here you can find almost anything and adapt it for your scenario.

Demo scripts for gnuplot (with images of output)
http://www.gnuplot.info/demo/

gnuplot Quick Reference (.pdf)
http://www.gnuplot.info/docs_4.0/gpcard.pdf

Plotting functions
http://www.gnuplotting.org/plotting-functions/

A Brief Manual and Tutorial
http://people.duke.edu/~hpgavin/gnuplot.html

gnuplot FAQ
http://www.gnuplot.info/faq/faq.html

Official gnuplot documentation
http://www.gnuplot.info/documentation.html

Oh the joy of coding with German Office

So I’m maintaining an Access database, with lots of VBA code, which serves as an internal management tool.

Changing a report should be, and usually is, pretty straight forward. But there I am today, after all changes are done, stuck trying to understand WHY THE FREAKING F*** a format string doesn’t work.

The offender is a text box with a date, and I’m trying to get it to be displayed like Nov-2015. So, according to Microsoft’s documentation, the format string is mmm-yyyy. Needless to say, didn’t work.

After an hour or so of banging my head on the wall, enlightenment comes: Year in German is Jahr !!! So mmm-jjjj, and, pronto, it worked like a charm.

By the way, Microsoft’s german doc is wrong (seems like a copy-paste error): it mentions jj and yyyy, instead of jj and jjjj which work (giving 15 and 2015 respectively).

GRRRRRRRRRRRRRRRRRRR *#@$%

How to overload static methods in C#

Let’s say I have an abstract generic class and a descendant:

public abstract class AuditObject<T> : ActiveRecordBase<T>;

(yes I’m using ActiveRecord) and

public class Employee : AuditObject<Employee>

In both of them I define some static Methods, e.g.

public static DataTable GetLookupTable(String where, Int32 topRows)
{
  return doExtremelyCleverStuffToFetchData(where, topRows);
}

(in the Employee class you need public new static or else you get a compiler warning)

As the code is, when I call e.g.

DataTable myList = AuditObject<T>.GetLookupTable("inactive = 0", 100);

…and T is Employee, the static method is not “overriden” i.e. the one that is executed is the method in AuditObject, not Employee .So in AuditObject I modified the static methods (in this example, GetLookupTable) like this :

public static DataTable GetLookupTable(String where, Int32 topRows)
{
  DataTable tbl = null;
  Boolean hasOverride = hasMethodOverride("GetLookupTable");
  if (hasOverride)
  {
    tbl = invokeStaticMethod<T>("GetLookupTable", new Object[2] { where, topRows }) as DataTable;
  }
  else
  {
    tbl = doExtremelyCleverStuffToFetchData(where, topRows);
  }
  return tbl;
}

Here’s how I find out if the static method exists :

private static Boolean hasMethodOverride(String methodName)
{
  var methodQuery =
    from method in typeof(T).GetMethods(
    BindingFlags.Static | BindingFlags.Public | BindingFlags.InvokeMethod)
    where method.Name == methodName
    select method;
  return methodQuery.Count() > 0;
}

And here’s how the “override” method is called :

public static Object invokeStaticMethod<T>(String MethodName, Object[] Args)
{
return typeof(T).InvokeMember(MethodName,
  BindingFlags.Public | BindingFlags.Static | BindingFlags.InvokeMethod,
  null, null, Args);
}

Voila ! When I call, say, DataTable myList = AuditObject<T>.GetLookupTable(“inactive = 0”, 100); and T is Employee, I get results from the static method defined in the Employee class.