The SQL Sentry Console is now 64-bit capable

I wanted to take a departure from the language-based posts I’ve done in the past and relay some information regarding the next release of our product. Starting with the next point release of our software (currently slated to be 4.3) The SQL Sentry Console will be able to run in native 64-bit mode. The reason for this blog post is to describe some of the reasons why this is available now and has not been in the past, as well as what it means to the end-user.

SQL Sentry has two components, the SQL Sentry Console, and the SQL Sentry Server Service. Each one of these talks to a number of different systems and uses many supporting dlls/assemblies to provide support for external systems. The SQL Sentry Server Service has run natively in 64-bit mode for some time now. The console, however has been forced to run in 32-bit mode. The reason for this is that in Windows, any 64-bit process can only load 64-bit dlls. You can’t mix and match 64-bit and 32-bit code.

SQL Sentry was conceived when SQL Server 2000 was the dominant SQL Server version. As such we decided early on to support reading SQL Server Enterprise Manager registrations into the console using SQL-DMO. We also found we could (with some work) show Enterprise Manager property windows and dialogs using the SQL-NS library. Both of these libraries were COM libraries, and since SQL Server 2000 was written at a time when 32-bit was your only OS option, the COM libraries were 32-bit. Eventually Microsoft added support for 64-bit operating systems in SQL Server 2000, but the client tools, running in 32-bit mode anyway, had no need to get these updates.

Because the console linked directly to these dlls to support reading registrations and showing SQL Server 2000 dialogs, the console was forced to run in 32-bit mode, lest it not be able to load the 32-bit dlls. This wasn’t a major issue to do, as it’s easy to flag an executable to run in x86 mode (vs. the default automatic detection mode for managed applications) by just setting that as a compilation option. It worked and that’s how SQL Sentry has been able to interoperate with SQL Server 2000 until now.

In 4.2 we wanted to support reading SQL Server 2008 registrations. This proved to be quite an engineering task as we found that Microsoft changed many of the APIs used to read in this registration data. Because of this we decided to go back to the drawing board and reengineer the way we read in registration information. As stated previously, before we linked directly to the registration COM objects (for SQL Server 2000) and SMO assemblies (for 2005). For 4.2 we elected to use an intermediate layer. We abstracted all the functionality we needed into a set of interfaces that we could read/write to, and then created plugins, one for 2000, one for 2005, and one for 2008. That allowed us to independently manage all the plugins and their corresponding references and decouple their implementations from the console. It was an undertaking but it paid off, because we have a much better separation of code layers, and we also will be able to support the next version of SQL Server without any major work.

Around the time when I’d looked at the feasibility of making the console work in 64-bit mode I quickly realized that doing so would require such a decoupling, because I had to get the 32-bit dlls out of the console process. It just so happens that the work done for 4.2 did just that.

In 4.3 the default build will not have the 32-bit flag in the manifest, so it will launch using whatever architecture the processor/OS supports. The side effect of this is if you are using the SQL Sentry Console on a 64-bit system and running it in 64-bit mode, you will be unable to read in SQL Server 2000 registrations, because it will not load the 2000 plugin (if it did it wouldn’t work due to the 64-bit/32-bit process/dll interoperability issue). The workaround for this is that we’re also shipping an x86 SQL Sentry Console that is flagged to run in x86 mode. This console will only be installed on 64-bit operating systems. If you install SQL Sentry on a 64-bit OS starting with 4.3 you’ll see two executable shortcuts in the start menu:

SQL Sentry Console and
SQL Sentry Console (x86)

If you require interoperation with SQL Server Enterprise Manager registrations, you should run the x86 version, otherwise, run the regular SQL Sentry Console, which will run in 64-bit mode on a 64-bit OS.

Dictionary Replication

It is very common in programming to need to do a replication of data. In SQL Sentry when we pull objects from remote systems we need to figure out if they exist in our database. We index objects by specific keys, and then during the synchronization process use these keys and compare them to the remote objects keys to figure out what objects are new, what objects have been deleted, and what objects have changed. The details of everything we do are beyond the scope of this article, but I find myself doing enough of these dictionary replications that I decided to blog about it.

Take the following scenario:
You have two dictionaries,

Dictionary<K,VTarget> targetDictionary
and
Dictionary<K,VSource> sourceDictionary

You want to in one call update targetDictionary with all the contents of sourceDictionary, and be able to generate callbacks for new entries, deleted entries, and changed entries. The value types are different, as you plan to map VSource to VTarget (more on that later), but they share a common key data type (we could later expand that to be different too if it suited us). It seems a bit overwhelming but it’s a perfect example of where generics can make your life a lot easier. Traditionally I’d find myself writing three loops. In the first loop I update changed items and add new items that are in the source but not in the target. In the second l find the keys that are in the target but not in the source. These are deleted items. I cant remove them yet though because I’m inside an enumerator and that would generate an error, so I use a temp collection then do one more loop at the end to remove them from the target.

   1: // Initialize the collections

   2: Dictionary<int, string> peopleByIDTarget = new Dictionary<int, string>();

   3: Dictionary<int, string> peopleByIDSource = new Dictionary<int, string>();

   4:  

   5: peopleByIDTarget.Add(1, "Brooke");

   6: peopleByIDTarget.Add(2, "Tommy");

   7:  

   8: peopleByIDSource.Add(2, "Rick");

   9: peopleByIDSource.Add(3, "Dom");

  10:  

  11: // Loop through the source

  12: foreach (KeyValuePair<int, string> sourceKeyValuePair in peopleByIDSource)

  13: {

  14:     string existingName;

  15:     

  16:     if (peopleByIDTarget.TryGetValue(sourceKeyValuePair.Key, out existingName))

  17:     {

  18:         // ID Exists. Change Name!

  19:         peopleByIDTarget[sourceKeyValuePair.Key] = sourceKeyValuePair.Value;

  20:     }

  21:     else

  22:     {

  23:         // ID doesn't exist, so add with name.

  24:         peopleByIDTarget.Add(sourceKeyValuePair.Key, sourceKeyValuePair.Value);

  25:     }

  26: }

  27:  

  28: // Create a temp list to hold items we need to remove. You cant remove items

  29: // while enumerating or you get an error.

  30: List<int> keysToRemove = new List<int>();

  31:  

  32: // Loop through the target to see what items dont exist in the source

  33: foreach (KeyValuePair<int, string> targetKeyValuePair in peopleByIDTarget)

  34: {

  35:     // The target item doesnt exist in the source so we must remove it.

  36:     // Add it to the removal list.

  37:     if (!peopleByIDSource.ContainsKey(targetKeyValuePair.Key))

  38:     {

  39:         keysToRemove.Add(targetKeyValuePair.Key);

  40:     }

  41: }

  42:  

  43: // Remove the keys we marked for removal

  44: foreach (int key in keysToRemove)

  45: {

  46:     peopleByIDTarget.Remove(key);

  47: }

This works but it’s quite a bit of code, especially if this is happening with a lot of collections. I like to promote code reuse so the goal was to make this routine generic so that I could simply call:

peopleByIDTarget.Merge(peopleByIDSource);

Another thing the above example lacks is support for the callbacks I mentioned earlier. I’d like to know when an item is removed, added, or changed, and specify it in a easily defined way, like

peopleByIDTarget.Merge(peopleByIDSource, itemAddedCallback, itemChangedCallback, itemRemovedCallback)

and get the item that was removed, added, or changed.

It’s pretty straightforward to convert the above code into a generic method. The following is the most advanced version, supporting lots of options, callbacks, comparisons to see whether two values are the same (you may not always wish to fire the changed event if the instance of V didn’t have any properties that are different).

First we need to define some helper classes for the callbacks:

   1: /// <summary>

   2: /// Provides event arguments for items that are added to a dictionary.

   3: /// </summary>

   4: /// <typeparam name="K">The Key type</typeparam>

   5: /// <typeparam name="V">The Value type</typeparam>

   6: public class DictionaryItemAddedEventArgs<K, V> : EventArgs

   7: {

   8:     /// <summary>

   9:     /// The Key

  10:     /// </summary>

  11:     public K Key { get; private set; }

  12:  

  13:     /// <summary>

  14:     /// The new value

  15:     /// </summary>

  16:     public V NewValue { get; private set; }

  17:  

  18:     /// <summary>

  19:     /// Creates a new DictionaryItemAddedEventArgs

  20:     /// </summary>

  21:     /// <param name="key">The key</param>

  22:     /// <param name="newValue">The new value</param>

  23:     public DictionaryItemAddedEventArgs(K key, V newValue)

  24:     {

  25:         this.Key = key;

  26:         this.NewValue = newValue;

  27:     }

  28: }

  29:  

  30: /// <summary>

  31: /// Provides event arguments for items that are changed in a dictionary.

  32: /// </summary>

  33: /// <typeparam name="K">The Key type</typeparam>

  34: /// <typeparam name="V">The Value type</typeparam>

  35: public class DictionaryItemChangedEventArgs<K, V> : EventArgs

  36: {

  37:     /// <summary>

  38:     /// The Key

  39:     /// </summary>

  40:     public K Key{ get; private set; }

  41:  

  42:     /// <summary>

  43:     /// The previous value

  44:     /// </summary>

  45:     public V OldValue { get; private set; }

  46:  

  47:     /// <summary>

  48:     /// The new value

  49:     /// </summary>

  50:     public V NewValue { get; private set; }

  51:  

  52:     /// <summary>

  53:     /// Creates a new DictionaryItemChangedEventArgs

  54:     /// </summary>

  55:     /// <param name="key">The key</param>

  56:     /// <param name="oldValue">The previous value</param>

  57:     /// <param name="newValue">The new value</param>

  58:     public DictionaryItemChangedEventArgs(K key, V oldValue, V newValue)

  59:     {

  60:         this.Key = key;

  61:         this.OldValue = oldValue;

  62:         this.NewValue = newValue;

  63:     }

  64: }

  65:  

  66: /// <summary>

  67: /// Provides event arguments for items that are deleted from a dictionary.

  68: /// </summary>

  69: /// <typeparam name="K">The Key type</typeparam>

  70: /// <typeparam name="V">The Value type</typeparam>

  71: public class DictionaryItemDeletedEventArgs<K, V> : EventArgs

  72: {

  73:     /// <summary>

  74:     /// The Key

  75:     /// </summary>

  76:     public K Key { get; private set; }

  77:  

  78:     /// <summary>

  79:     /// The previous value

  80:     /// </summary>

  81:     public V OldValue { get; private set; }

  82:  

  83:     /// <summary>

  84:     /// Creates a new DictionaryItemDeletedEventArgs

  85:     /// </summary>

  86:     /// <param name="key">The key</param>

  87:     /// <param name="oldValue">The previous value</param>

  88:     public DictionaryItemDeletedEventArgs(K key, V oldValue)

  89:     {

  90:         this.Key = key;

  91:         this.OldValue = oldValue;

  92:     }

  93: }

Then we can get to the actual dictionary extensions class. The primary work starts on line 180 and I've included a couple other helper extensions I added for other uses:

   1: /// <summary>

   2: /// Provides extention methods to the dictionary class

   3: /// </summary>

   4: public static class DictionaryExtensions

   5: {

   6:     /// <summary>

   7:     /// Creates a new Dictionary with the key and value of the current dictionary reversed.

   8:     /// This method should be not used when duplicate values are expected because collisions will occur.

   9:     /// </summary>

  10:     /// <typeparam name="K">The Key type</typeparam>

  11:     /// <typeparam name="V">The Value type</typeparam>

  12:     /// <param name="dictionary">The dictionary to use</param>

  13:     /// <returns>A Dictionary with the keys and values of the current dictionary reversed</returns>

  14:     public static Dictionary<V, K> CreateDictionaryOfValueAndKey<K, V>(this Dictionary<K, V> dictionary)

  15:     {

  16:         Dictionary<V, K> result = new Dictionary<V,K>();

  17:         foreach (KeyValuePair<K, V> keyValuePair in dictionary)

  18:         {

  19:             result.Add(keyValuePair.Value, keyValuePair.Key);

  20:         }

  21:  

  22:         return result;

  23:     }

  24:  

  25:     /// <summary>

  26:     /// Creates a new MultiDictionary with the key and value of the current dictionary reversed.

  27:     /// This method should be used when duplicate values are expected.

  28:     /// </summary>

  29:     /// <typeparam name="K">The Key type</typeparam>

  30:     /// <typeparam name="V">The Value type</typeparam>

  31:     /// <param name="dictionary">The dictionary to use</param>

  32:     /// <returns>A MultiDictionary with the keys and values of the current dictionary reversed</returns>

  33:     public static MultiDictionary<V, K> CreateMultiDictionaryOfValueAndKey<K, V>(this Dictionary<K, V> dictionary)

  34:     {

  35:         MultiDictionary<V, K> result = new MultiDictionary<V, K>();

  36:         foreach (KeyValuePair<K, V> keyValuePair in dictionary)

  37:         {

  38:             result.Add(keyValuePair.Value, keyValuePair.Key);

  39:         }

  40:  

  41:         return result;

  42:     }

  43:  

  44:     /// <summary>

  45:     /// Merges the targetDictionary with the sourceDictionary, deleting items that arent in sourceDictionary, 

  46:     /// adding items that are in sourceDictionary but not in the targetDictionary, and updating items that are in both, 

  47:     /// setting them to the value in sourceDictionary

  48:     /// </summary>

  49:     /// <typeparam name="K">The Key type</typeparam>

  50:     /// <typeparam name="V">The Value type of the source and target dictionaries</typeparam>        

  51:     /// <param name="targetDictionary">The current dictionary to merge entries into</param>

  52:     /// <param name="sourceDictionary">The new dictionary with the most recent data</param>

  53:     public static void Merge<K, V>(

  54:         this Dictionary<K, V> targetDictionary,

  55:         Dictionary<K, V> sourceDictionary)

  56:     {

  57:         Merge(targetDictionary, sourceDictionary, null, null, null, null, null);

  58:     }

  59:  

  60:     /// <summary>

  61:     /// Merges the targetDictionary with the sourceDictionary, deleting items that arent in sourceDictionary, 

  62:     /// adding items that are in sourceDictionary but not in the targetDictionary, and updating items that are in both, 

  63:     /// setting them to the value in sourceDictionary

  64:     /// </summary>

  65:     /// <typeparam name="K">The Key type</typeparam>

  66:     /// <typeparam name="VTarget">The Value type of the target dictionary</typeparam>

  67:     /// <typeparam name="VSource">The Value type of the source dictionary</typeparam>

  68:     /// <param name="targetDictionary">The current dictionary to merge entries into</param>

  69:     /// <param name="sourceDictionary">The new dictionary with the most recent data</param>

  70:     public static void Merge<K, VTarget, VSource>(

  71:         this Dictionary<K, VTarget> targetDictionary,

  72:         Dictionary<K, VSource> sourceDictionary)

  73:     {

  74:         Merge(targetDictionary, sourceDictionary, null, null, null, null, null);

  75:     }

  76:  

  77:     /// <summary>

  78:     /// Merges the targetDictionary with the sourceDictionary, deleting items that arent in sourceDictionary, 

  79:     /// adding items that are in sourceDictionary but not in the targetDictionary, and updating items that are in both, 

  80:     /// setting them to the value in sourceDictionary

  81:     /// </summary>

  82:     /// <typeparam name="K">The Key type</typeparam>

  83:     /// <typeparam name="V">The Value type of the source and target dictionaries</typeparam>

  84:     /// <param name="targetDictionary">The current dictionary to merge entries into</param>

  85:     /// <param name="sourceDictionary">The new dictionary with the most recent data</param>

  86:     /// <param name="valueUpdater">The action to use to update values that share the same key</param>

  87:     public static void Merge<K, V>(

  88:         this Dictionary<K, V> targetDictionary,

  89:         Dictionary<K, V> sourceDictionary,

  90:         Func<V, V, bool> valueUpdater)

  91:     {

  92:         Func<V, V> valueMapper = x => x;

  93:         Merge(targetDictionary, sourceDictionary, valueMapper, valueUpdater, null, null, null);

  94:     }

  95:  

  96:     /// <summary>

  97:     /// Merges the targetDictionary with the sourceDictionary, deleting items that arent in sourceDictionary, 

  98:     /// adding items that are in sourceDictionary but not in the targetDictionary, and updating items that are in both, 

  99:     /// setting them to the value in sourceDictionary

 100:     /// </summary>

 101:     /// <typeparam name="K">The Key type</typeparam>

 102:     /// <typeparam name="VTarget">The Value type of the target dictionary</typeparam>

 103:     /// <typeparam name="VSource">The Value type of the source dictionary</typeparam>

 104:     /// <param name="targetDictionary">The current dictionary to merge entries into</param>

 105:     /// <param name="sourceDictionary">The new dictionary with the most recent data</param>

 106:     /// <param name="valueMapper">The transform to convert VSource to VTarget</param>

 107:     /// <param name="valueUpdater">The action to use to update values that share the same key</param>

 108:     public static void Merge<K, VTarget, VSource>(

 109:         this Dictionary<K, VTarget> targetDictionary,

 110:         Dictionary<K, VSource> sourceDictionary,

 111:         Func<VSource, VTarget> valueMapper,

 112:         Func<VTarget, VTarget, bool> valueUpdater)

 113:     {

 114:         Merge(targetDictionary, sourceDictionary, valueMapper, valueUpdater, null, null, null);

 115:     }

 116:  

 117:     /// <summary>

 118:     /// Merges the targetDictionary with the sourceDictionary, deleting items that arent in sourceDictionary, 

 119:     /// adding items that are in sourceDictionary but not in the targetDictionary, and updating items that are in both, 

 120:     /// setting them to the value in sourceDictionary

 121:     /// </summary>

 122:     /// <typeparam name="K">The Key type</typeparam>

 123:     /// <typeparam name="V">The Value type of the source and target dictionaries</typeparam>

 124:     /// <param name="targetDictionary">The current dictionary to merge entries into</param>

 125:     /// <param name="sourceDictionary">The new dictionary with the most recent data</param>

 126:     /// <param name="itemAddedEventHandler">The event to fire for items that were added</param>

 127:     /// <param name="itemChangedEventHandler">The event to fire for items that were changed</param>

 128:     /// <param name="itemDeletedEventHandler">The event to fire for items that were deleted</param>

 129:     public static void Merge<K, V>(

 130:         this Dictionary<K, V> targetDictionary,

 131:         Dictionary<K, V> sourceDictionary,

 132:         EventHandler<DictionaryItemAddedEventArgs<K, V>> itemAddedEventHandler,

 133:         EventHandler<DictionaryItemChangedEventArgs<K, V>> itemChangedEventHandler,

 134:         EventHandler<DictionaryItemDeletedEventArgs<K, V>> itemDeletedEventHandler)

 135:     {

 136:         Func<V, V> valueMapper = x => x;

 137:         Merge(targetDictionary, sourceDictionary, valueMapper, null, itemAddedEventHandler, itemChangedEventHandler, itemDeletedEventHandler);

 138:     }

 139:  

 140:     /// <summary>

 141:     /// Merges the targetDictionary with the sourceDictionary, deleting items that arent in sourceDictionary, 

 142:     /// adding items that are in sourceDictionary but not in the targetDictionary, and updating items that are in both, 

 143:     /// setting them to the value in sourceDictionary

 144:     /// </summary>

 145:     /// <typeparam name="K">The Key type</typeparam>

 146:     /// <typeparam name="VTarget">The Value type of the target dictionary</typeparam>

 147:     /// <typeparam name="VSource">The Value type of the source dictionary</typeparam>

 148:     /// <param name="targetDictionary">The current dictionary to merge entries into</param>

 149:     /// <param name="sourceDictionary">The new dictionary with the most recent data</param>

 150:     /// <param name="valueMapper">The transform to convert VSource to VTarget</param>

 151:     /// <param name="itemAddedEventHandler">The event to fire for items that were added</param>

 152:     /// <param name="itemChangedEventHandler">The event to fire for items that were changed</param>

 153:     /// <param name="itemDeletedEventHandler">The event to fire for items that were deleted</param>

 154:     public static void Merge<K, VTarget, VSource>(

 155:         this Dictionary<K, VTarget> targetDictionary,

 156:         Dictionary<K, VSource> sourceDictionary,

 157:         Func<VSource, VTarget> valueMapper,

 158:         EventHandler<DictionaryItemAddedEventArgs<K, VTarget>> itemAddedEventHandler,

 159:         EventHandler<DictionaryItemChangedEventArgs<K, VTarget>> itemChangedEventHandler,

 160:         EventHandler<DictionaryItemDeletedEventArgs<K, VTarget>> itemDeletedEventHandler)

 161:     {

 162:         Merge(targetDictionary, sourceDictionary, valueMapper, null, itemAddedEventHandler, itemChangedEventHandler, itemDeletedEventHandler);

 163:     }        

 164:  

 165:     /// <summary>

 166:     /// Merges the targetDictionary with the sourceDictionary, deleting items that arent in sourceDictionary, 

 167:     /// adding items that are in sourceDictionary but not in the targetDictionary, and updating items that are in both, 

 168:     /// setting them to the value in sourceDictionary

 169:     /// </summary>

 170:     /// <typeparam name="K">The Key type</typeparam>

 171:     /// <typeparam name="VTarget">The Value type of the target dictionary</typeparam>

 172:     /// <typeparam name="VSource">The Value type of the source dictionary</typeparam>

 173:     /// <param name="targetDictionary">The current dictionary to merge entries into</param>

 174:     /// <param name="sourceDictionary">The new dictionary with the most recent data</param>

 175:     /// <param name="valueMapper">The transform to convert VSource to VTarget</param>

 176:     /// <param name="valueUpdater">The action to use to update values that share the same key</param>

 177:     /// <param name="itemAddedEventHandler">The event to fire for items that were added</param>

 178:     /// <param name="itemChangedEventHandler">The event to fire for items that were changed</param>

 179:     /// <param name="itemDeletedEventHandler">The event to fire for items that were deleted</param>

 180:     public static void Merge<K, VTarget, VSource>(

 181:         this Dictionary<K, VTarget> targetDictionary,

 182:         Dictionary<K, VSource> sourceDictionary,

 183:         Func<VSource, VTarget> valueMapper,

 184:         Func<VTarget, VTarget, bool> valueUpdater,

 185:         EventHandler<DictionaryItemAddedEventArgs<K, VTarget>> itemAddedEventHandler,

 186:         EventHandler<DictionaryItemChangedEventArgs<K, VTarget>> itemChangedEventHandler,

 187:         EventHandler<DictionaryItemDeletedEventArgs<K, VTarget>> itemDeletedEventHandler)

 188:     {

 189:         foreach (var keyValuePair in sourceDictionary)

 190:         {

 191:             VTarget newValue = valueMapper(keyValuePair.Value);

 192:  

 193:             VTarget oldValue;

 194:             if (targetDictionary.TryGetValue(keyValuePair.Key, out oldValue))

 195:             {

 196:                 bool changed = true;

 197:                 if (valueUpdater == null)

 198:                 {

 199:                     targetDictionary[keyValuePair.Key] = newValue;

 200:                 }

 201:                 else

 202:                 {

 203:                     changed = valueUpdater(oldValue, newValue);

 204:                 }

 205:  

 206:                 if (itemChangedEventHandler != null && changed)

 207:                 {

 208:                     itemChangedEventHandler(targetDictionary, new DictionaryItemChangedEventArgs<K, VTarget>(keyValuePair.Key, oldValue, newValue));

 209:                 }

 210:             }

 211:             else

 212:             {

 213:                 targetDictionary.Add(keyValuePair.Key, newValue);

 214:                 if (itemAddedEventHandler != null)

 215:                 {

 216:                     itemAddedEventHandler(targetDictionary, new DictionaryItemAddedEventArgs<K, VTarget>(keyValuePair.Key, newValue));

 217:                 }

 218:             }

 219:         }

 220:  

 221:         List<KeyValuePair<K, VTarget>> itemsToDelete = new List<KeyValuePair<K, VTarget>>();

 222:         foreach (var keyValuePair in targetDictionary)

 223:         {

 224:             if (!sourceDictionary.ContainsKey(keyValuePair.Key))

 225:             {

 226:                 itemsToDelete.Add(keyValuePair);

 227:             }

 228:         }

 229:  

 230:         foreach (var keyValuePair in itemsToDelete)

 231:         {

 232:             targetDictionary.Remove(keyValuePair.Key);

 233:             if (itemDeletedEventHandler != null)

 234:             {

 235:                 itemDeletedEventHandler(targetDictionary, new DictionaryItemDeletedEventArgs<K, VTarget>(keyValuePair.Key, keyValuePair.Value));

 236:             }

 237:         }

 238:     }

 239: }

It’s essentially the original code, just made generic with the callbacks included. There are some additional Func<> delegates. valueMapper is used to transform the source value type to the target value type if they are different. Note there are overloads that do not require this and they just use a simple x=>x mapping. Also, there is a valueUpdater delegate as well. It is used to compare two values to see if they are really the same, which is useful if the value type is a class with properties and you want to see if those have changed prior to calling the changed callback.

Taking the initial example we can now do this:

   1: int countRemoved = 0;

   2: int countAdded = 0;

   3: int countChanged = 0;

   4:  

   5: peopleByIDTarget.Merge(

   6: peopleByIDSource,

   7: (dictionary, itemAddedArgs) =>

   8: {

   9:     countAdded++;

  10:     System.Diagnostics.Debug.WriteLine("Item " + itemAddedArgs.NewValue + " Added");

  11: },

  12: (dictionary, itemChangedArgs) =>

  13: {

  14:     countChanged++;

  15:     System.Diagnostics.Debug.WriteLine("Item " + itemChangedArgs.OldValue + " changed to " + itemChangedArgs.NewValue);

  16: },

  17: (dictionary, itemRemovedArgs) =>

  18: {

  19:     countRemoved++;

  20:     System.Diagnostics.Debug.WriteLine("Item " + itemRemovedArgs.OldValue + " Removed");

  21: });

  22:  

  23: System.Diagnostics.Debug.WriteLine(countAdded.ToString() + " Items Added");

  24: System.Diagnostics.Debug.WriteLine(countChanged.ToString() + " Items Changed");

  25: System.Diagnostics.Debug.WriteLine(countRemoved.ToString() + " Items Removed");

Generics combined with closures allows for some very rapid development.