C++ 示例：使用复杂类型

UDx 可以接受和返回复杂类型。ArraySlice 示例将一个数组和两个索引作为输入，返回一个仅包含该范围内的值的数组。由于数组元素可以是任何类型，因此函数是多态的。

完整的源代码位于 /opt/vertica/sdk/examples/ScalarFunctions/ArraySlice.cpp 中。

加载和使用示例

加载库并创建函数，如下所示：

=> CREATE OR REPLACE LIBRARY ScalarFunctions AS '/home/dbadmin/examplesUDSF.so';

=> CREATE FUNCTION ArraySlice AS
LANGUAGE 'C++' NAME 'ArraySliceFactory' LIBRARY ScalarFunctions;

创建一些数据并在其上调用函数，如下所示：

=> CREATE TABLE arrays (id INTEGER, aa ARRAY[INTEGER]);
COPY arrays FROM STDIN;
1|[]
2|[1,2,3]
3|[5,4,3,2,1]
\.

=> CREATE TABLE slices (b INTEGER, e INTEGER);
COPY slices FROM STDIN;
0|2
1|3
2|4
\.

=> SELECT id, b, e, ArraySlice(aa, b, e) AS slice FROM arrays, slices;
 id | b | e | slice
----+---+---+-------
  1 | 0 | 2 | []
  1 | 1 | 3 | []
  1 | 2 | 4 | []
  2 | 0 | 2 | [1,2]
  2 | 1 | 3 | [2,3]
  2 | 2 | 4 | [3]
  3 | 0 | 2 | [5,4]
  3 | 1 | 3 | [4,3]
  3 | 2 | 4 | [3,2]
(9 rows)

工厂实施

由于函数是多态的，getPrototype() 声明输入和输出可以是任何类型，类型强制必须在别处完成：

void getPrototype(ServerInterface &srvInterface,
                              ColumnTypes &argTypes,
                              ColumnTypes &returnType) override
{
    /*
     * This is a polymorphic function that accepts any array
     * and returns an array of the same type
     */
    argTypes.addAny();
    returnType.addAny();
}

工厂验证输入类型并确定 getReturnType() 中的返回类型：

void getReturnType(ServerInterface &srvInterface,
                   const SizedColumnTypes &argTypes,
                   SizedColumnTypes &returnType) override
{
    /*
     * Three arguments: (array, slicebegin, sliceend)
     * Validate manually since the prototype accepts any arguments.
     */
    if (argTypes.size() != 3) {
        vt_report_error(0, "Three arguments (array, slicebegin, sliceend) expected");
    } else if (!argTypes[0].getType().isArrayType()) {
        vt_report_error(1, "Argument 1 is not an array");
    } else if (!argTypes[1].getType().isInt()) {
        vt_report_error(2, "Argument 2 (slicebegin) is not an integer)");
    } else if (!argTypes[2].getType().isInt()) {
        vt_report_error(3, "Argument 3 (sliceend) is not an integer)");
    }

    /* return type is the same as the array arg type, copy it over */
    returnType.push_back(argTypes[0]);
}

函数实施

使用 BlockReader 和 BlockWriter 调用 processBlock() 方法。第一个实参是一个数组。为了访问数组的元素，该方法使用 ArrayReader。同样，它使用 ArrayWriter 来构造输出。

void processBlock(ServerInterface &srvInterface,
        BlockReader &argReader,
        BlockWriter &resWriter) override
{
    do {
        if (argReader.isNull(0) || argReader.isNull(1) || argReader.isNull(2)) {
            resWriter.setNull();
        } else {
            Array::ArrayReader argArray  = argReader.getArrayRef(0);
            const vint slicebegin = argReader.getIntRef(1);
            const vint sliceend   = argReader.getIntRef(2);

            Array::ArrayWriter outArray = resWriter.getArrayRef(0);
            if (slicebegin < sliceend) {
                for (int i = 0; i < slicebegin && argArray->hasData(); i++) {
                    argArray->next();
                }
                for (int i = slicebegin; i < sliceend && argArray->hasData(); i++) {
                    outArray->copyFromInput(*argArray);
                    outArray->next();
                    argArray->next();
                }
            }
            outArray.commit();  /* finalize the written array elements */
        }
        resWriter.next();
    } while (argReader.next());
}