Table of Contents

Expressions Any fields and actions supports expressions

What is a expression?

Expression is a simple way to return a dynamic value from a string.

How it works?

Expressions can return a boolean or a object value at runtime
Example:

"val:1" Return true.
"val:0" Return false.
"exp:1=1" Return true.
"exp: {IsList}" If at the list state return true
"exp:'{pagestate}' = 'UPDATE' AND '{ID}' = '1'" If update and a field value ID equals 1 return true

Don't forget to add single quotes, if your value is a string or can be null, because it will be replaced at runtime

In the Data Dictionary UI, the expression editor is simplified like this: Customized Fields

What are the default expression providers?

  • Type [val:] returns a value; (1 or 0) (true or false) ("foo") etc..
  • Type [exp:] returns the result of the expression from NCalc;
  • Type [sql:] returns the result of a sql command;
Tip

Check if your field supports all expressions checking the attributes of the desired property at the docs.

Tip

SQL Expression values will be replaced with a SQL variable to prevent SQL injection attacks.

How to do it?

Building an expression

Warning

Contents enclosed in {} (braces) will be replaced by current values at runtime. Following the order:

MasterData keywords

  • {PageState} = "INSERT" | "UPDATE" | "VIEW" | "LIST" | "FILTER" | "IMPORT"
  • {IsList} = 1 | 0
  • {IsFilter} = 1 | 0
  • {IsView} = 1 | 0
  • {IsInsert} = 1 | 0
  • {IsUpdate} = 1 | 0
  • {IsDelete} = 1 | 0
  • {IsImport} = 1 | 0
  • {ComponentName} = Name of the component that the field resides
  • {FieldName} = Name of the field that triggered the AutoPostBack event
  • {UserId} = Identifier of the authenticated user, can be recovered from UserValues, Session or Claims

Dynamic values will be recovered in the following order:

  1. MasterData keywords
  2. UserValues
  3. FormValues
  4. UserSession
  5. Claims

Examples

Example using [val:] + text

  1. val:a simple text;
  2. val:10000;
var field = new ElementField();
field.DefaultValue = "val:test";

Example using [exp:] + expression

  1. exp:'{field1}';
  2. exp:({field1} + 10) * {field2};
var field = new ElementField();
field.DefaultValue = "exp:{UserId}";

Example using [sql:] + query

  1. sql:select 'foo';
  2. sql:select count(*) from table1;
var field = new ElementField();
//In the runtime this will be replaced with select field2 from table1 where field1 = @field1
field.DefaultValue = "sql:select field2 from table1 where field1 = '{field1}'";

Types of Expressions

  • Default Value: When the value is null or empty, this expression will execute before the trigger to populate the value
  • Trigger Expression: This is always executed after an AJAX request to reload the form or when the form is first opened.
  • Visible Expression: Controls the field visibility, and must return a bool value.
  • Enable Expression: Controls if the field is enabled or not, if the field is disabled, the value is not sent to the server, and must return a bool value.

Implementing your own expression provider

You can implement both <xref:JJMasterData.Core.DataManager.Expressions.Abstractions.IBooleanExpressionProvider> (used at visible and enable expressions) or IAsyncExpressionProvider (used at triggers and default values.).

You can call ExpressionHelper to replace values {} with runtime values.

At your Program.cs simply:

builder.Services.AddJJMasterDataWeb().WithExpressionProvider<TMyCustomProvider>();

Executing C# code at your expressions

You can execute C# code using the following example;

Program.cs:

builder.Services.PostConfigure<MasterDataCoreOptions>(options =>
{
    options.ExpressionsContext.Functions = new Dictionary<string, ExpressionFunction>
    {
        {"now", _ => DateTime.Now},
        {"myAwesomeFunction", args => MyCustomClass.Execute(args[0], args[1])}
    }.ToFrozenDictionary()
});

At your expression:

exp: myAwesomeFunction('{StringValue}',{IntValue})
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