Global Expression method

[frankiDotNet]

Hello,

Is there any way to create mapping with an ExpressionMethodAttribute and call a method that is not defined in the class itself? Say that I couod call a global defined method in multiple classes for mapping.
In my case I would like to map a property to a column if it exists, if my database version is older and the column does not exists in this version, I would overwrite thr mapping for this property to an ExpressionMethod that receives the default value.

// column exists 
[Column("Test")]
Public string TestProperty{ get; set}

// column does not exist
[ExpressionMethod("DefaultStringValueMethod"), IsColumn= true]
Public string TestProperty {get; set;}

[sdanyliv]

@Franki1986, so this approach do not works for you?

[frankiDotNet]

This works, but so I have to write every time a new query. If I could overcome this directly in mapping it would be easier. This is no feauture request I know that this is not an every day use case, but if there is the possibilty I would use it. Also if i do a where condition on a property that has nocolumm attribute, won't this fail?
Any way to call global methods?

[sdanyliv]

I do not see possiblity. Expression method expects appropriate type for entity, but you can always create dynamic method generator that of course should be marked as expression method.
Everything that you have mentioned you can do by our T4 scripts. Add attribute, add method to the entity wih body. Everything.

[frankiDotNet]

Ok, there is no problem until there is a way for a solution. Thanks for your investigation!

[frankiDotNet]

Ok I have played around a bit and this seems to work good:

<#@ template language="C#" debug="True" hostSpecific="True"                          #>
<#@ output extension=".generated.cs"                                                 #>
<#@ assembly name="$(ProjectDir)\bin\Debug\AssemblyWithAllTableClasses"#>
<#@ assembly name="$(ProjectDir)\bin\Debug\linq2db.dll"#>

<#@ import namespace="NamespaceOfAllTableClasses"   #>
<#@ assembly name="System.Core"                   #>
<#@ import namespace="System"                     #>
<#@ import namespace="System.Reflection"   #>
<#@ import namespace="System.Collections"   #>
<#@ import namespace="System.Collections.Generic" #>
<#@ import namespace="System.Linq"                #>
<#@ import namespace="LinqToDB.Mapping"   #>

<#
	var assemblyNameContainingMappings = "AssemblyWithAllTableClasses";
	var ms = new MappingSchema();
	WriteLine("using System;");
	WriteLine("using System.Linq.Expressions;");
	WriteLine("using LinqToDB;");
	WriteLine("");
	WriteLine("");	
       
       // I think in next Version of Linq2Db we can use new 'MappingSchema().MetadataReader.GetMappedTypes()'
	var assemblyContainigMappings =	AppDomain.CurrentDomain.GetAssemblies().SingleOrDefault(assembly => assembly.GetName().Name == assemblyNameContainingMappings);
	if(assemblyContainigMappings != null){
		foreach (var type in assemblyContainigMappings.GetTypes())
		{
			var tableAttribut = ms.GetAttributes<TableAttribute>(type, type).FirstOrDefault();
			if (tableAttribut != null)
			{		
				var namespaceOfClass = type.Namespace;
				WriteLine("namespace " + namespaceOfClass + " {");
				WriteLine("");
				WriteLine(String.Format("\tpublic partial class {0} {{ \t", type.Name));

				WriteLine(String.Format("\t\tpublic static Expression<Func<{0}, DateTime>> Default_DateTime()", type.Name));
				WriteLine("\t\t{");
				WriteLine("\t\t\treturn x => Sql.CurrentTimestamp;");
				WriteLine("\t\t}");

				WriteLine(String.Format("\t\tpublic static Expression<Func<{0}, Int32>> Default_Int32()", type.Name));
				WriteLine("\t\t{");
				WriteLine("\t\t\treturn x => 0;");
				WriteLine("\t\t}");
				
				WriteLine(String.Format("\t\tpublic static Expression<Func<{0}, UInt32>> Default_UInt32()", type.Name));
				WriteLine("\t\t{");
				WriteLine("\t\t\treturn x => (UInt32)0;");
				WriteLine("\t\t}");

				WriteLine(String.Format("\t\tpublic static Expression<Func<{0}, Int16>> Default_Int16()", type.Name));
				WriteLine("\t\t{");
				WriteLine("\t\t\treturn x => (Int16)0;");
				WriteLine("\t\t}");

				WriteLine(String.Format("\t\tpublic static Expression<Func<{0}, UInt16>> Default_UInt16()", type.Name));
				WriteLine("\t\t{");
				WriteLine("\t\t\treturn x => (UInt16)0;");
				WriteLine("\t\t}");

				WriteLine(String.Format("\t\tpublic static Expression<Func<{0}, object>> Default_Nullable()", type.Name));
				WriteLine("\t\t{");
				WriteLine("\t\t\treturn x => null;");
				WriteLine("\t\t}");

				WriteLine(String.Format("\t\tpublic static Expression<Func<{0}, string>> Default_String()", type.Name));
				WriteLine("\t\t{");
				WriteLine("\t\t\treturn x => \"\";");
				WriteLine("\t\t}");

				WriteLine("\t}");

				WriteLine("");			
				WriteLine("}");
			}
		}
	}
#>

The only thing that does not work is, if a property is nullable:

[ExpressionMethod("Default_Nullable")]
      public DateTime? ToDelete { get; set; }

      static Expression<Func<Kunde, DateTime?>> Default_Nullable()
      {
         return (c) => null;
      }

Is there a problem with this expression?

[frankiDotNet]

Closed with this solution DateTime-Nullable