feature suggest: simplify the example class generated

[WestFarmer]

currently, the generated example can be relatively large and lacking support of free forms of SQL conditions:

for example:

`(A or B) and C`

is not directly supported, we need to convert it as :

`(A and C) or (B and C)`

I suggest a recursive way to represent SQL conditions:

public class Filter {
	
	private String field;
        // 'and' | 'or'
	private FilterLogic logic;

	private FilterOperator operator;

	private Object value;

	private List<Filter> filters;
        
       // getters and setters
}

then add it to example class, also add a method to generate where clause, I believe it's not possible to do so with xml, because xml elements not support recursive structure.

 // --- drat implementations not fully tested ---
public String getWhereClause() {
	return convertFilterToSQL(filter, 0, new int[filter.getDepth()]);
}

private String convertFilterToSQL(Filter filter, int depth, int[] idxs) {
		String buffer = "";
		String field = filter.getField();
		if (field != null) {
			String left = getColumn(field);
			String chain = getChainedValueExpression(field, depth, idxs);
			// boolean types in database can be used as condition directly
			if (filter.getOperator() == null) {
				buffer += left;
			} else if (filter.getOperator() == FilterOperator.IN || filter.getOperator() == FilterOperator.NOT_IN) {
				Object o = filter.getValue();
				List<Object> os = (List<Object>) o;
				String[] ss = new String[os.size()];
				for (int i = 0; i < os.size(); i++) {
					ss[i] = "#{filter" + chain + ".value[" + i + "]}";
				}
				buffer += left + " " + filter.getOperator().getSQLCondition() + " " + StringUtil.join(ss, "(", ", ", ")");
			} else if (filter.getOperator() == FilterOperator.BETWEEN || filter.getOperator() == FilterOperator.NOT_BETWEEN) {
				buffer += left + " " + filter.getOperator().getSQLCondition() + " #{filter" + chain + ".value[0]} and #{filter" + chain + ".value[1]}";
			} else if (filter.getOperator() == FilterOperator.IS_NULL || filter.getOperator() == FilterOperator.IS_NOT_NULL) {
				buffer += left + " " + filter.getOperator().getSQLCondition();
			} else {
				buffer += left + " " + filter.getOperator().getSQLCondition() + " #{filter" + chain + ".value}";
			}

		} else if (filter.getLogic() == FilterLogic.OR) {
			String[] ss = new String[filter.getFilters().size()];
			for (int i = 0; i < filter.getFilters().size(); i++) {
				idxs[depth] = i;
				ss[i] = convertFilterToSQL(filter.getFilters().get(i), depth + 1, idxs);

			}
			buffer += StringUtil.join(ss, "(", " or ", ")");
		} else if (filter.getLogic() == FilterLogic.AND) {
			String[] ss = new String[filter.getFilters().size()];
			for (int i = 0; i < filter.getFilters().size(); i++) {
				idxs[depth] = i;
				ss[i] = convertFilterToSQL(filter.getFilters().get(i), depth + 1, idxs);
			}
			buffer += StringUtil.join(ss, "(", " and ", ")");
		}
		return buffer;
	}

private String getChainedValueExpression(String field, int depth, int[] idxs) {
		System.out.println(depth + ":" + StringUtil.join(idxs, "[", ", ", "]"));
		if (depth == 0) {
			return ".";
		} else {
			String s = "";
			for (int i = 0; i < depth; i++) {
				s += ".filters[" + idxs[i] + "]";
			}
			return s;
		}
	}

then use it in xmls:

<if test="_parameter.filter != null">
where ${_parameter.getWhereClause()}
</if>

and we also need a fluent api to build filters.

[jeffgbutler]

Please take a look at the newer generator runtimes that generate code for https://github.com/mybatis/mybatis-dynamic-sql. The XML based generators are deprecated because - as you say - XML based code is very brittle and low function. I built the new runtimes to address issues like you are raising here.