[ksqlDB.RestApi.Client]: enabled specifying of pseudocolumns using the Fluent API's model builder #96

Author: tomasfabian

ksqlDb.RestApi.Client/FluentAPI/Builders/FieldTypeBuilder.cs

@@ -45,6 +45,12 @@ public interface IFieldTypeBuilder<TProperty>
     /// </summary>
     /// <returns>The field type builder for chaining additional configuration.</returns>
     IFieldTypeBuilder<TProperty> AsStruct();
+
+    /// <summary>
+    /// Marks the field as a ksqldb pseudocolumn.
+    /// </summary>
+    /// <returns>The field type builder for chaining additional configuration.</returns>
+    IFieldTypeBuilder<TProperty> AsPseudoColumn();
   }
 
   internal class FieldTypeBuilder<TProperty>(FieldMetadata fieldMetadata)
@@ -62,6 +68,12 @@ public IFieldTypeBuilder<TProperty> AsStruct()
       return this;
     }
 
+    public IFieldTypeBuilder<TProperty> AsPseudoColumn()
+    {
+      fieldMetadata.IsPseudoColumn = true;
+      return this;
+    }
+
     public IFieldTypeBuilder<TProperty> Ignore()
     {
       fieldMetadata.Ignore = true;

ksqlDb.RestApi.Client/KSql/RestApi/Parsers/IdentifierUtil.cs

@@ -56,10 +56,10 @@ internal static string Format(MemberExpression memberExpression, IdentifierEscap
       return escaping switch
       {
         Never => memberExpression.GetMemberName(metadataProvider),
-        Keywords when memberExpression.Member.GetCustomAttribute<PseudoColumnAttribute>() != null => memberExpression.Member.Name,
+        Keywords when IsPseudoColumn(memberExpression.Member, metadataProvider) => memberExpression.Member.Name,
         Keywords when IsValid(memberExpression.GetMemberName(metadataProvider)) && SystemColumns.IsValid(memberExpression.GetMemberName(metadataProvider)) => memberExpression.GetMemberName(metadataProvider),
         Keywords => string.Concat("`", memberExpression.GetMemberName(metadataProvider), "`"),
-        Always when memberExpression.Member.GetCustomAttribute<PseudoColumnAttribute>() != null => memberExpression.Member.Name,
+        Always when IsPseudoColumn(memberExpression.Member, metadataProvider) => memberExpression.Member.Name,
         Always => string.Concat("`", memberExpression.GetMemberName(metadataProvider), "`"),
         _ => throw new ArgumentOutOfRangeException(nameof(escaping), escaping, "Non-exhaustive match.")
       };
@@ -82,13 +82,26 @@ public static string Format(MemberInfo memberInfo, IdentifierEscaping escaping,
       return escaping switch
       {
         Never => memberInfo.GetMemberName(modelBuilder),
-        Keywords when memberInfo.GetCustomAttribute<PseudoColumnAttribute>() != null => memberInfo.Name,
+        Keywords when IsPseudoColumn(memberInfo, modelBuilder) => memberInfo.Name,
         Keywords when IsValid(memberInfo.GetMemberName(modelBuilder)) && SystemColumns.IsValid(memberInfo.GetMemberName(modelBuilder)) => memberInfo.GetMemberName(modelBuilder),
         Keywords => string.Concat("`", memberInfo.GetMemberName(modelBuilder), "`"),
-        Always when memberInfo.GetCustomAttribute<PseudoColumnAttribute>() != null => memberInfo.Name,
+        Always when IsPseudoColumn(memberInfo, modelBuilder) => memberInfo.Name,
         Always => string.Concat("`", memberInfo.GetMemberName(modelBuilder), "`"),
         _ => throw new ArgumentOutOfRangeException(nameof(escaping), escaping, "Non-exhaustive match.")
       };
     }
+
+    private static bool IsPseudoColumn(MemberInfo memberInfo, IMetadataProvider? metadataProvider)
+    {
+      if (memberInfo.GetCustomAttribute<PseudoColumnAttribute>() != null)
+        return true;
+
+      var entityMetadata = metadataProvider?.GetEntities().FirstOrDefault(c => c.Type == memberInfo.DeclaringType);
+
+      var fieldMetadata =
+        entityMetadata?.FieldsMetadata.FirstOrDefault(c => c.MemberInfo.Name == memberInfo.Name);
+
+      return fieldMetadata is {IsPseudoColumn: true};
+    }
   }
 }

ksqlDb.RestApi.Client/Metadata/FieldMetadata.cs

@@ -23,6 +23,7 @@ public FieldMetadata(FieldMetadata fieldMetadata)
     internal bool IgnoreInDDL { get; set; }
     public bool HasHeaders { get; internal set; }
     internal bool IsStruct { get; set; }
+    public bool IsPseudoColumn { get; internal set; }
     internal string Path { get; init; } = null!;
     internal string FullPath { get; init; } = null!;
     public string? ColumnName { get; set; }