System.Xml.Schema.Compiler.CompileIdentityConstraint C# (CSharp) Method

        private void CompileIdentityConstraint (XmlSchemaIdentityConstraint xi) { 
            if (xi.IsProcessing) {
                xi.CompiledConstraint = CompiledIdentityConstraint.Empty;       
                SendValidationEvent(Res.Sch_IdentityConstraintCircularRef, xi);
                return;
            }

            if (xi.CompiledConstraint != null) {
                return;
            }
            
            xi.IsProcessing = true;
            CompiledIdentityConstraint compic = null;
            try {
                SchemaNamespaceManager xnmgr = new SchemaNamespaceManager(xi);
                compic = new CompiledIdentityConstraint(xi, xnmgr);
                if (xi is XmlSchemaKeyref) {
                    XmlSchemaIdentityConstraint ic = (XmlSchemaIdentityConstraint)this.identityConstraints[((XmlSchemaKeyref)xi).Refer];
                    if (ic == null) {
                        throw new XmlSchemaException(Res.Sch_UndeclaredIdentityConstraint, ((XmlSchemaKeyref)xi).Refer.ToString(), xi);
                    }     
                    CompileIdentityConstraint(ic);
                    if (ic.CompiledConstraint == null) {
                        throw new XmlSchemaException(Res.Sch_RefInvalidIdentityConstraint, ((XmlSchemaKeyref)xi).Refer.ToString(), xi);
                    }
                    // keyref has the different cardinality with the key it referred
                    if (ic.Fields.Count != xi.Fields.Count) {
                        throw new XmlSchemaException(Res.Sch_RefInvalidCardin, xi.QualifiedName.ToString(), xi);
                    }
                    // keyref can only refer to key/unique
                    if (ic.CompiledConstraint.Role == CompiledIdentityConstraint.ConstraintRole.Keyref) {
                        throw new XmlSchemaException(Res.Sch_ReftoKeyref, xi.QualifiedName.ToString(), xi);
                    }
                }
                xi.CompiledConstraint = compic;
            }
            catch (XmlSchemaException e) {
                if (e.SourceSchemaObject == null) {
                    e.SetSource(xi);
                }
                SendValidationEvent(e);
                xi.CompiledConstraint = CompiledIdentityConstraint.Empty;       
                // empty is better than null here, stop quickly when circle referencing
            } 
            finally {
                xi.IsProcessing = false;
            }

        }