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IIndexSet<T> is the initial interface you must implement if you wish to implement your own CSLA .NET indexing provider. Table 14-4 shows the required members for IIndexSet. CSLA .NET base collection classes such as BusinessListBase<C, T> and ReadOnlyListBase<C, T> know how to leverage this interface to take advantage of indexing.
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Table 14-4. IIndexSet Members
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InsertItem(T item) InsertItem(T item, string property) RemoveItem(T item) RemoveItem(T item, string property)
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Description
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The index item on all indexable properties The index item only on property if it is indexable Removes the item from all indices Removes the item only from the index specified by property
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CHAPTER 14 LINQ TO C SLA
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Table 14-4. IIndexSet Members (Continued)
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ReindexItem(T item) ReindexItem(T item, string property) ClearIndexes() ClearIndex(string property) Search(Expression expr) this [string property] Load(string property)
Description
Removes and adds the item from all indices Removes and adds the item from a specific index Clears all the indices for all properties Clears a specific index Performs a search, filtering by expr Returns the IIndex<T> specified by property Creates an index on property over the source
IIndexSet needs to have a reference to the IEnumerable collection that it is indexing, such as BusinessListBase and other CSLA .NET collection classes. When you write a class that supports IIndexSet, you are typically managing the set of IIndex objects (individual indices, described in the following sections) that constitute the index set, and providing the logic for performing the search to determine whether the query can use an index. You can think of the classes that implement this interface is coordinators for all indexing activity. Classes should evaluate the expression tree passed to Search(), determine the correct index to use (if applicable), and then either use the index (if it is an indexed property) or perform the search on the original collection (if there is no available index).
IndexSet
The IndexSet concrete class represents the default index provider implementation for CSLA .NET. The class maintains a set of indices appropriate for the property types that it is indexing. It provides an implementation of Search() that determines the IComparable status of the property being searched, determines the operation being used (such as equality and less-than operations), and assures that the appropriate operation is called on the index. This class provides an example of most of the expression evaluation techniques I have talked about previously in this chapter. For example, the following method in the IndexSet class determines the value on the right side of the expression passed to Search(): private object GetRightValue(Expression rightSide) { //rightside is where I get the value... switch (rightSide.NodeType) { //shortcut constants, don't eval these, it will be faster case ExpressionType.Constant: ConstantExpression constExp = (ConstantExpression)rightSide; return (constExp.Value); // convert back to lambda and eval to get the value. default: //Lambdas can be created from expressions... LambdaExpression evalRight = Expression.Lambda(rightSide, null); //Compile it, invoke it, and get the resulting value return (evalRight.Compile().DynamicInvoke(null)); } }
CHAPTER 14 LINQ TO C SLA
The key to this code is looking at the type of node you re dealing with. All Expression objects implement the NodeType property, which gives you clues about the nature of the Expression you re dealing with. You now care about only two real cases: whether you have a ConstantExpression, allowing you to bypass a more expensive call to Compile() and DynamicInvoke(), or whether you do not have a constant, in which case you ll have to compile the expression, invoke it, and get the value that it will ultimately return. In either case, you get back an object that boxes the value you want to use in the Search() operation.
Note
Compile() and DynamicInvoke() are expensive operations to conduct. You don t want to be doing these operations on a per-item basis as you search through a data structure.
Determining whether you have an index or not is much simpler. bool IIndexSet<T>.HasIndexFor(string property) { return _internalIndexSet.ContainsKey(property); } private bool HasIndexablePropertyOnLeft(Expression leftSide) { if (leftSide.NodeType == ExpressionType.MemberAccess) return ( this as IIndexSet<T>).HasIndexFor(((MemberExpression)leftSide).Member.Name ); else return false; } Determining whether you have an index for a given property specified by a string is relatively simple, as you have an internal field _internalIndexSet that is really just a Dictionary of indices. You can call ContainsKey() on the _internalIndexSet to determine whether you have the index. The examination of the expression that represents the left side of the total expression is slightly more complex. You need for this left-side expression to be a MemberExpression in order to make any sense of it. Thankfully, this is common, given that it rarely makes sense to have anything other than a MemberExpression on the left side. Note that this may be possible technically (i.e., x => 1 == 1 can be passed, which, in theory, would return all results). The first thing you do is test the NodeType to ensure that it s a MemberAccess expression. If that is in fact the case, you know you can cast it to a MemberExpression, which then gives you access to the name of the property you re looking at (such as the name SomeProp on the left side, which is in an expression such as x => x.SomeProp == 42). With this information, you have everything you need to determine whether or not you have an index on the property. Once you have established that you have a property that is Indexable and a value to check against the index, you can test the operation between both sides of the expression to determine which index operation to perform. Func<T, bool> exprCompiled = expr.Compile(); BinaryExpression binExp = (BinaryExpression)expr.Body; object val = GetRightValue(binExp.Right); IRangeTestableIndex<T> rangedIndex; if (_internalIndexSet[property] is IRangeTestableIndex<T>) { rangedIndex = (IRangeTestableIndex<T>)_internalIndexSet[property];
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