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Parser Schemas– Easy and Powerful parsing of XML-based languages

, 18 Oct 2005
An article on parsing XML files according to the specified schema.
/***********************************************************************\
 * Comnicate.CodeDom.Xml.ParserSchemas                                 *
 * Parses xml-based languages according to a user defined schema.      *
 * Copyright � 2005 Tomas Deml (as Comnicate!)                         *
 *                  tomasdeml@msn.com                                  *
 *                                                                     *
 * This library is free software; you can redistribute it and/or       *
 * modify it under the terms of the GNU Lesser General Public          *
 * License as published by the Free Software Foundation; either        *
 * version 2.1 of the License, or (at your option) any later version.  *
 *                                                                     *
 * This library is distributed in the hope that it will be useful,     *
 * but WITHOUT ANY WARRANTY; without even the implied warranty of      *
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU   *
 * Lesser General Public License for more details.                     *
\***********************************************************************/

using System;
using System.Collections.Generic;
using System.Text;
using System.Xml.XPath;
using System.Xml;
using Comnicate.CodeDom.Xml.ParserSchemas.Rules;
using Comnicate.CodeDom.Xml.ParserSchemas.Rules.Evaluated;
using Comnicate.CodeDom.Xml.ParserSchemas.Rules.Evaluation;

namespace Comnicate.CodeDom.Xml.ParserSchemas
{
    /// <summary>
    /// Represents the results of a schema evaluation.
    /// </summary>
    public class EvaluatedParserSchema : ParserSchema
    {
        #region Fields

        // Default namespace prefix
        private const string NamespacePrefix = "ns";

        // Evaluated parent rule
        private EvaluatedParentalRule evaluatedParentRule;

        #endregion

        #region .ctors

        /// <summary>
        /// Initializes a new instance of the <see cref="EvaluatedParserSchema"/> class.
        /// </summary>
        /// <param name="evaluatedParentNode">Evaluated parent node rule.</param>
        /// <param name="rawParentRule">Original (not evaluated) parent node rule.</param>
        private EvaluatedParserSchema(EvaluatedParentalRule evaluatedParentNode, ParentalRule rawParentRule) : base(rawParentRule)
        {
            // Check for null...
            if (evaluatedParentNode == null) throw new ArgumentNullException("evaluatedParentNode");

            // Init fields
            this.evaluatedParentRule = evaluatedParentNode;
            base.ParentNode = rawParentRule;
        }

        #endregion

        #region Properties

        /// <summary>
        /// Gets the evaluated parent rule. You can access its children using this property.
        /// </summary>
        public new EvaluatedParentalRule ParentNode
        {
            get
            {
                return this.evaluatedParentRule;
            }
        }

        #endregion

        #region Methods

        /// <summary>
        /// Evaluates the schema and return results.
        /// </summary>
        /// <param name="schema">Schema to evaluate.</param>
        /// <param name="documentNavigator">An instance of the <see cref="XPathNavigator"/> class representing the Xml document.</param>
        /// <param name="matchOption">Specifies if the <paramref name="documentNavigator"/> points to the parent node that will be matched by the <see cref="ParentNode"/> rule or if it points to the parent of the parent node that will be matched by the <see cref="ParentNode"/> rule.</param>
        /// <returns>Evaluation results as an instance of the <see cref="EvaluatedParserSchema"/> class.</returns>
        public static EvaluatedParserSchema EvaluateSchema(ParserSchema schema, XPathNavigator documentNavigator, ParentNodeMatchOption matchOption)
        {
            try
            {
                // Check args...
                if (schema == null) throw new ArgumentNullException("schema");
                if (documentNavigator == null) throw new ArgumentNullException("documentNavigator");
                if (!Enum.IsDefined(typeof(ParentNodeMatchOption), matchOption)) throw new ArgumentOutOfRangeException("matchOption");

                // If the provided schema was already evaluated...
                if (schema is EvaluatedParserSchema) throw new InvalidOperationException(Resources.ExceptionMsg_SchemaAlreadyEvaluated);

                // Make a copy of the document navigator (we do not want to change user's navigator)
                XPathNavigator ourDocumentNavigator = documentNavigator.Clone();

                // XmlNamespaceManager
                XmlNamespaceManager manager = null;

                // If the parent node is "namespaced"...
                if (schema.ParentNode.NamespaceUri != null)
                {
                    // Init XmlNamespaceManager according to the document to parse
                    manager = new XmlNamespaceManager(ourDocumentNavigator.NameTable);

                    // Add the namespace of the parent node
                    manager.AddNamespace(NamespacePrefix, schema.ParentNode.NamespaceUri.ToString());
                }

                // If the XPathNavigator already points to the parent node, point it to its parent...
                if (matchOption == ParentNodeMatchOption.NavigatorPointsToParentNode)
                    ourDocumentNavigator.MoveToParent();

                // Parent navigator
                XPathNavigator parentNavigator = null;

                // If we have to consider namaspaces...
                if (manager != null)
                    // Select a node with name and in namespace specified by the parent node rule
                    parentNavigator = ourDocumentNavigator.SelectSingleNode(String.Format("{0}:{1}", NamespacePrefix, schema.ParentNode.NodeName), manager);
                else
                    // Select a node with name specified by the parent node rule
                    parentNavigator = ourDocumentNavigator.SelectSingleNode(schema.ParentNode.NodeName);

                // No node matching to the parent node rule found...
                if (parentNavigator == null)
                    throw new ValidationException(String.Format(Resources.ExceptionMsg_Formatable1_ParentNodeNotFound, schema.ParentNode), schema.ParentNode, parentNavigator, null);

                // Evaluate the parent node rule (and its children)
                EvaluatedParentalRule evaluatedParentRule = schema.ParentNode.Evaluate(parentNavigator);

                // Construct the resulting schema
                EvaluatedParserSchema resultSchema = new EvaluatedParserSchema(evaluatedParentRule, schema.ParentNode);

                // Return evaluated schema
                return resultSchema;
            }
            catch (ValidationException vE)
            {
                throw new ValidationException(String.Format(Resources.ExceptionMsg_Formatable1_InvalidDocument, vE.Message), vE);
            }
            catch (Exception e)
            {
                throw new InvalidOperationException(String.Format(Resources.ExceptionMsg_Formatable1_SchemaCannotBeEvaluated, e.Message), e);
            }
        }

        #endregion
    }
}

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About the Author

Tomas Deml

Czech Republic Czech Republic
I'm a student of the Low-voltage Electrical Engineering specialized on Computing from the Czech republic.
 
I'm a C# kind of guy, fan of .NET.
 
I've formed a programming group called 'Comnicate!'. Currently the only member of the group is myself. Wink | ;-)

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