Examples of org.apache.derby.iapi.types.SqlXmlUtil

org.apache.derby.iapi.types.SqlXmlUtil
This class contains "utility" methods that work with XML-specific objects that are only available if JAXP and/or Xalan are in the classpath. NOTE: This class is only compiled with JDK 1.4 and higher since the XML-related classes that it uses (JAXP and Xalan) are not part of earlier JDKs. Having a separate class for this functionality is beneficial for two reasons: 1. Allows us to allocate XML objects and compile an XML query expression a single time per statement, instead of having to do it for every row against which the query is evaluated. An instance of this class is created at compile time and then passed (using "saved objects") to the appropriate operator implementation method in XML.java; see SqlXmlExecutor.java for more about the role this class plays in "saved object" processing. 2. By keeping all XML-specific references in this one class, we have a single "point of entry" to the XML objects--namely, the constructor for this class. Thus, if we always make sure to check for the required XML classes _before_ calling this class's constructor, we can detect early on whether some classes (ex. Xalan) are missing, and can throw a friendly error up front, instead of a ClassNotFoundException somewhere deeper in the execution codepath. The initial check for the required XML classes can be found in XML.checkXMLRequirements(). Note that we don't want to put references to XML-specific objects directly into XML.java because that class (XML.java) is instantiated anytime a table with an XML column is referenced. That would mean that if a user tried to select a non-XML column (ex. integer) from a table that had at least one XML column in it, the user would have to have JAXP and Xalan classes in his/her classpath--which we don't want. Instead, by keeping all XML-specific objects in this one class, and then only instantiating this class when an XML operator is used (either implicitly or explicitly), we make it so that the user is only required to have XML-specific classes in his/her classpath _if_ s/he is trying to access or operate on XML values.


        // Create a new XML compiler object; the constructor
        // here automatically creates the XML-specific objects 
        // required for parsing/serializing XML, so all we
        // have to do is create an instance.
        sqlxUtil = new SqlXmlUtil();


        // The result type of XMLParse() is always an XML type.
        setType(DataTypeDescriptor.getBuiltInDataTypeDescriptor(
            StoredFormatIds.XML_TYPE_ID));
    }

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        // Create a new XML compiler object; the constructor
        // here automatically creates the XML-specific objects 
        // required for parsing/serializing XML, so all we
        // have to do is create an instance.
        sqlxUtil = new SqlXmlUtil();


        // The result type of XMLParse() is always an XML type.
        setType(DataTypeDescriptor.getBuiltInDataTypeDescriptor(
            StoredFormatIds.XML_TYPE_ID));
    }

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            throw StandardException.newException(
                SQLState.LANG_INVALID_XML_QUERY_EXPRESSION);
        }
        else {
        // compile the query expression.
            sqlxUtil = new SqlXmlUtil();
            sqlxUtil.compileXQExpr(
                ((CharConstantNode)leftOperand).getString(),
                (operatorType == XMLEXISTS_OP ? "XMLEXISTS" : "XMLQUERY"));
        }

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        // Create a new XML compiler object; the constructor
        // here automatically creates the XML-specific objects 
        // required for parsing/serializing XML, so all we
        // have to do is create an instance.
        sqlxUtil = new SqlXmlUtil();


        // The result type of XMLParse() is always an XML type.
        setType(DataTypeDescriptor.getBuiltInDataTypeDescriptor(
                JDBC40Translation.SQLXML));
    }

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            throw StandardException.newException(
                SQLState.LANG_INVALID_XML_QUERY_EXPRESSION);
        }
        else {
        // compile the query expression.
            sqlxUtil = new SqlXmlUtil();
            sqlxUtil.compileXQExpr(
                ((CharConstantNode)leftOperand).getString(),
                (operatorType == XMLEXISTS_OP ? "XMLEXISTS" : "XMLQUERY"));
        }

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        // Create a new XML compiler object; the constructor
        // here automatically creates the XML-specific objects 
        // required for parsing/serializing XML, so all we
        // have to do is create an instance.
        sqlxUtil = new SqlXmlUtil();


        // The result type of XMLParse() is always an XML type.
        setType(DataTypeDescriptor.getBuiltInDataTypeDescriptor(
                JDBC40Translation.SQLXML));
    }

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            throw StandardException.newException(
                SQLState.LANG_INVALID_XML_QUERY_EXPRESSION);
        }
        else {
        // compile the query expression.
            sqlxUtil = new SqlXmlUtil();
            sqlxUtil.compileXQExpr(
                ((CharConstantNode)leftOperand).getString(),
                (operatorType == XMLEXISTS_OP ? "XMLEXISTS" : "XMLQUERY"));
        }

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            throw StandardException.newException(
                SQLState.LANG_INVALID_XML_QUERY_EXPRESSION);
        }
        else {
        // compile the query expression.
            sqlxUtil = new SqlXmlUtil();
            sqlxUtil.compileXQExpr(
                ((CharConstantNode)leftOperand).getString(),
                (operatorType == XMLEXISTS_OP ? "XMLEXISTS" : "XMLQUERY"));
        }

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        // Create a new XML compiler object; the constructor
        // here automatically creates the XML-specific objects 
        // required for parsing/serializing XML, so all we
        // have to do is create an instance.
        sqlxUtil = new SqlXmlUtil();


        // The result type of XMLParse() is always an XML type.
        setType(DataTypeDescriptor.getBuiltInDataTypeDescriptor(
            StoredFormatIds.XML_TYPE_ID));
    }

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