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App_Code/Shared/FormulaEvaluator.vb
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App_Code/Shared/FormulaEvaluator.vb
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Imports Microsoft.VisualBasic
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Imports System.IO
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Imports BaseClasses.Data
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Imports Ciloci.Flee
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Imports Persons.UI
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Imports Persons.Data
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Namespace Persons
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''' <summary>
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''' The FormulaEvaluator class evaluates a formula passed to the Evaluate function.
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''' You must set the DataSource and Page variables as part of this.
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''' </summary>
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''' <remarks></remarks>
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Public Class FormulaEvaluator
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Inherits BaseFormulaEvaluator
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''' <summary>
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''' Record control (or row) from which this evaluator is called. Could be Nothing
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''' if called from the data access layer.
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''' </summary>
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Private _callingControl As Control = Nothing
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Public Property CallingControl() As Control
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Get
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Return _callingControl
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End Get
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Set(ByVal value As Control)
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_callingControl = value
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End Set
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End Property
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''' <summary>
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''' Create a new evaluator and prepare for evaluation.
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''' </summary>
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Public Sub New(Optional ByVal mainObj As Object = Nothing)
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' pass mainObj to contructor so that formula like = mainObj.<functionName> can be evaluated
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If mainObj Is Nothing Then
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_evaluator = New ExpressionContext()
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Else
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_evaluator = New ExpressionContext(mainObj)
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End If
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' The order of adding types is important. First we add our own
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' formula functions, followed by the generic types.
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Evaluator.Imports.AddType(GetType(BaseFormulaUtils))
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Evaluator.Imports.AddType(GetType(FormulaUtils))
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' ADVANCED. For advanced usage, generic types can also be imported into
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' the formula evaluator. This is done by adding types of some generic types
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' such as Math, DateTime, Convert, and String. For example, if you add the
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' Convert type, you can then use Convert.ToDecimal("string"). The second
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' parameter to the AddType is the namespace that will be used in the formula.
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' These functions expect a certain type. For example, Math functions expect
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' a Double for the most part. If you pass a string, they will throw an exception.
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' As such, we have written separate functions in FormulaUtils that are more
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' loosely-typed than the standard libraries available here.
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' Examples:
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Evaluator.Imports.AddType(GetType(Math), "Math")
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Evaluator.Imports.AddType(GetType(DateTime), "DateTime")
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Evaluator.Imports.AddType(GetType(Convert), "Convert")
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Evaluator.Imports.AddType(GetType(String), "String")
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' We want a loosely-typed evaluation language - so do not
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' type-check any variables.
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Evaluator.Options.Checked = False
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' Our policy is to always treat real numbers as Decimal instead of
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' Double or Single to make it consistent across the entire
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' evaluator.
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Evaluator.Options.RealLiteralDataType = RealLiteralDataType.Decimal
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' The variable event handler handles the variables based on the DataSource.
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AddHandler _evaluator.Variables.ResolveVariableType, AddressOf variables_ResolveVariableType
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AddHandler _evaluator.Variables.ResolveVariableValue, AddressOf variables_ResolveVariableValue
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End Sub
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''' <summary>
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''' Evaluate the expression passed in as the string
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''' </summary>
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''' <param name="expression">The input whose absolute value is to be found.</param>
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''' <returns>The result of the evaluation. Can we be any data type including string, datetime, decimal, etc.</returns>
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Public Overrides Function Evaluate(ByVal expression As String) As Object
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If IsNothing(expression) Then Return Nothing
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If expression = "" Then Return ""
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' Strip of the = in the front of the forumula - the Expression evaluator
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' does not need it. Also, make sure to trim the result to remove any
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' spaces in the front and the back.
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expression = expression.TrimStart(New Char() {"="c, " "c}).Trim()
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' Add all realted controls of this control. This includes the calling control, its children and parents.
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AddRelatedControlVariables()
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' If there are any exceptions when parsing or evaluating, they are
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' thrown so that the end user can see the error. As such, there is no
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' Try-Catch block here.
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Try
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Dim eDynamic As IDynamicExpression = _evaluator.CompileDynamic(expression)
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Return eDynamic.Evaluate()
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Catch ex As Exception
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Return "ERROR: " & ex.Message
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End Try
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End Function
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#Region "Private functions"
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''' <summary>
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''' Adds related record and table controls.
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''' This has to navigate up to the page level and add any table or record controls.
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''' And we have to navigate within to add any record/table controls.
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''' And we have to go sideways to also add any controls.
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''' Finally we have to add the page control.
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''' This allows the expression to use any record or table control on the page
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''' as long as it is accessible without being in a repeater.
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''' </summary>
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Private Sub AddRelatedControlVariables()
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If IsNothing(CallingControl) Then Return
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Try
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' STEP 1: Our strategy is to first add the current control and
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' all of its parents. This way, we maintain the full context of where
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' we are. For example, if you are in a row within a table, within another row
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' that is within another table, then by going up the hierarchy looking for parents
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' will preserve all of the context.
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' Later in Step 2 we will go through the other branches.
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Dim ctl As Control = CallingControl
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While Not (IsNothing(ctl))
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If TypeOf ctl Is BaseApplicationRecordControl OrElse TypeOf ctl Is BaseApplicationTableControl Then
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AddControlAndChildren(ctl)
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End If
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' Navigate up.
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ctl = ctl.Parent
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End While
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' STEP 2: Go through the other branches on the page and add all other table and
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' record controls on the page.
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AddControlAndChildren(CallingControl.Page)
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' STEP 3: Add more variable for ASCX control.
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AddVariableNameWithoutUnderscore()
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' STEP 4: Finally add the Page itself.
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Evaluator.Variables.Add("Page", CallingControl.Page)
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Catch ex As Exception
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' Ignore and continue in case of a problem.
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End Try
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End Sub
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''' <summary>
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''' Add this control and all child controls of the given control.
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''' We only add the Record and Table Controls. No other controls need
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''' to be added.
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''' This function is smart enough not to add or descend down a control
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''' that was previously added by checking whether the Id is already contained
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''' in the Evaluator variables. This avoids unnecessary traversal.
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''' This function is called recursively to add any child controls.
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''' </summary>
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Private Sub AddControlAndChildren(ByVal ctl As Control)
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' We quit immediately if a control is already in the list of variables,
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' because we have convered that branch already.
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Try
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If IsNothing(ctl) Then Return
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If Not (IsNothing(ctl.ID)) AndAlso Evaluator.Variables.ContainsKey(ctl.ID) Then Return
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' If this is a record or table control, add it.
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If TypeOf ctl Is BaseApplicationRecordControl OrElse TypeOf ctl Is BaseApplicationTableControl Then
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If Not (IsNothing(ctl.ID)) Then
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Evaluator.Variables.Add(ctl.ID, ctl)
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End If
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End If
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For Each child As Control In ctl.Controls
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' We do not want to go into a repeater because there will be multiple rows.
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' So we will call AddChildControls only for those controls that are NOT repeaters.
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If Not (TypeOf child Is System.Web.UI.WebControls.Repeater) Then
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AddControlAndChildren(child)
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End If
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Next
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Catch ex As Exception
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' Ignore - we do not want to give an exception if we cannot add all variables.
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End Try
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End Sub
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''' <summary>
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''' If the current is not ASPX page but ASCX controls, the controls in this ASCX control has id starting with underscore.
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''' To avoid confusion in formula, we also define variable name without underscore.
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''' </summary>
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''' <remarks></remarks>
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Private Sub AddVariableNameWithoutUnderscore()
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Dim vars As New Collections.Generic.Dictionary(Of String, Object)
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Dim enumerator As Collections.Generic.IEnumerator(Of Collections.Generic.KeyValuePair(Of String, Object)) = Me.Evaluator.Variables.GetEnumerator()
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While enumerator.MoveNext
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If enumerator.Current.Key.StartsWith("_") Then
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Dim varNameWitoutUnderscore As String = enumerator.Current.Key.Substring(1)
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If Not Me.Evaluator.Variables.ContainsKey(varNameWitoutUnderscore) Then
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vars.Add(varNameWitoutUnderscore, enumerator.Current.Value)
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End If
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End If
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End While
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Dim enumerator2 As Collections.Generic.Dictionary(Of String, Object).Enumerator = vars.GetEnumerator()
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While enumerator2.MoveNext
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Me.Evaluator.Variables.Add(enumerator2.Current.Key, enumerator2.Current.Value)
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End While
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End Sub
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#End Region
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End Class
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End Namespace
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