ECExpressions

ECExpressions is a very basic language that allows customizing presentation rules' behavior.

Symbols that can be used depend on current context. Example:

this.GetContextB().ContextC.DoSomething()

Here, symbol this returns a context which has a function symbol GetContextB(). This function returns a context which has a property symbol ContextC. And the property value is a context that contains a function symbol DoSomething(). The latter function might return some value or return nothing, but instead do some action - it all depends on the symbol.

ECExpression Syntax

Data types

ECExpressions contain values of primitive types or data type of ECClass or ECArray.

Primitive value types

Other primitive types

ECClass data type

ECClass data types define ECInstances. ECClasses contain ECProperties and Methods which can be accessed via dot (.) operator.

ECArray data type

ECArray data types define arrays of values. Each value can be accessed via [] operator.

Expression components

In addition to values of primitive types ECExpressions may contain symbols and operators

Symbols

Symbols are used to supply values to expression evaluator. Symbols can be supplied from ECInstance via an access string, from an application defined value or from application defined method. Access string is a limited expression that holds no blanks, no operators, and no variable portions. It may contain array indexing and member selection using [] or dot . operators, but no part of the expression can be variable, and the access string cannot contain embedded blanks.

Property symbols

ECInstance Property symbols supply Property values of some ECInstance when the symbol is being evaluated.

this.PropertyName
this.StructPropertyName.PropertyName
this.StructArray[5].Struct.PropertyName

Value symbols

Value symbols supply some named predefined value in a context.

System.Math.PI

Method symbols

Method symbols supply a named method in a context.

System.Math.Sin(1.57)
this.IsOfClass("ClassName", "SchemaName")

Value Lists

Value lists in ECExpressions are iterable containers and can be handled with lambdas. Currently presentation rules engine supports only a single simple lambda for value lists, AnyMatches, which checks if any of the items in the value list passes given condition. Examples:

value_list.AnyMatches(x => x = this.PropertyValue)
value_list.AnyMatches(x => this.PropertyValue = x)
value_list.AnyMatches(x => this.IsOfClass(x.PropertyValue))

Operators

Parentheses (,)

(2 * (3 + 4))

Logical operators

Note: *Checks right side of expression even if result value can be deducted from the left side.

False And True OrElse True

Comparison operators

20 < 10 ==> False

Arithmetic operators

1 + "4"   ==> 5
2.2 * 3   ==> 6.6
12 / 5    ==> 2.4
12 \ 5    ==> 2
25 Mod 3  ==> 1

Bit Shift operators

5 << 1      ==>  10
24 >> 2     ==>  6
-105 >> 1   ==>  -53
-105 >>> 1  ==>  75

Conditional operator

IIf (condition, true-result, false-result)

Returns result based on given condition. If condition evaluates to true, returns true-result. Otherwise returns false-result.

IIf (500>200, "Math ok", "Math wrong") ==> "Math ok"
IIf (500<200, "Math ok", "Math wrong") ==> "Math wrong"

Concatenation operator

"Dog" & " and " & "Cat" ==> "Dog and Cat"
"1" & 4                 ==> "14"
1 & "4"                 ==> "14"

Lambda operator

Lambda operator => creates a callback expression for a given symbol.

MyArray.Find(item => item.IntProperty = 5)

Combined expressions

System.Math.Cos (System.Math.PI * 45.0 / 180.0) ==> 0.707
System.String.Length ("Dog" & " and " & "Cat") ==> 11

Evaluating if property is Null

Method IsNull (value) evaluates if given value is Null.

Method IfNull (value, value-if-null) evaluates to value if it is not null, otherwise evaluates to value-if-null.

In case this.MiddleName is null:

IfNull (this.MiddleName, "") ==> ""
IIf (Not IsNull(this.MiddleName), " " & this.MiddleName & " ", "") ==> ""

In case this.MiddleName is set to "Harvey"

IfNull (this.MiddleName, "") ==> "Harvey"
IIf (Not IsNull (this.MiddleName), " " & this.MiddleName & " ", "") ==> " Harvey "

Checking to see if a this.MiddleName is Null or empty

IIf (IsNull (this.MiddleName) or this.MiddleName = "", "Is null or empty", "Has a value")

ECExpression Contexts

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ECInstance

ECInstance expression context provides access to ECInstance property values. Example:

this.PropertyName
this.StructPropertyName.PropertyName
this.StructArray[1].Struct.PropertyName

Additionally, when evaluating ECInstance contexts, the below symbols are available:

Deprecated symbols:

ECInstance Key

ECInstance key expression context provides access to class and instance IDs. The context has the following symbols:

Symbols in Global Context

Ruleset Variables (User Settings)

Note: User Settings is a deprecated name of Ruleset Variables concept.

Ruleset variable access symbols allow accessing variable values through ECExpressions.

Other symbols

Formatted property values

Comparison of formatted property values in ECExpressions can be done using GetFormattedValue function. Specific unit system can be passed as a second argument to function or omitted to use default presentation format:

GetFormattedValue(this.Length, "Metric") = "10.0 m"
GetFormattedValue(this.Length) = "10.0 m"

Last Updated: 11 June, 2024