Automatic Construction of MyBatis-Plus QueryWrapper Using Reflection and Generics

Background : When building complex query conditions with MyBatis-Plus Wrapper, developers often spend excessive time manually writing each condition and may introduce errors.

Idea : Provide a generic method that inspects a parameter object's fields via reflection, determines the appropriate query operation based on the field type, and returns a correctly typed QueryWrapper instance.

Implementation : The method iterates over all declared fields of the supplied object, skips null values, resolves the database column name by checking for a @TableField annotation or converting camelCase to snake_case, and applies the appropriate condition ( like, eq, in, between) based on the field’s Java type. Helper code for camel‑to‑snake conversion is also included.

/**
 * 创建对应的wrapper
 * @param param 参数对象
 * @param <T> 范型
 * @return 创建好的wrapper
 */
public static <T> QueryWrapper<T> createWrapper(Object param) {
    QueryWrapper<T> wrapper = new QueryWrapper<>();
    Class<?> dataClass = param.getClass();
    try {
        for (Field field : dataClass.getDeclaredFields()) {
            field.setAccessible(true);
            //获取字段类型和字段值
            Class<?> type = field.getType();
            Object value = field.get(param);
            if (value == null) {
                continue;
            }
            //将字段名转为数据库中的字段名
            String fieldName;
            TableField tableFieldAnnotation = field.getAnnotation(TableField.class);
            if (tableFieldAnnotation != null) {
                fieldName = tableFieldAnnotation.value();
            } else {
                fieldName = convertToSnakeCase(field.getName());
            }
            //根据字段的类型来选择不同的查询方式
            if (type == String.class) {
                wrapper.like(fieldName, value);
            } else if (type == Long.class) {
                wrapper.eq(fieldName, value);
            } else if (type == List.class) {
                wrapper.in(fieldName, (List<?>)value);
            } else if (type == Between.class) {
                Between val = (Between) value;
                wrapper.between(fieldName, val.getStart(), val.getEnd());
            } else {
                wrapper.eq(fieldName, value);
            }
        }
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    }
    return wrapper;
}

/**
 * 将驼峰命名法的字段名转为下划线隔开的形式
 * @param input 驼峰命名法的字段名
 * @return 下划线隔开的数据库字段名
 */
private static String convertToSnakeCase(String input) {
    StringBuilder output = new StringBuilder();
    for (int i = 0; i < input.length(); i++) {
        char ch = input.charAt(i);
        if (Character.isUpperCase(ch)) {
            if (i > 0) {
                output.append(StrPool.C_UNDERLINE);
            }
            output.append(Character.toLowerCase(ch));
        } else {
            output.append(ch);
        }
    }
    return output.toString();
}

Test : After invoking createWrapper with a DTO instance, the generated QueryWrapper contains all non‑null fields mapped to the correct database columns and query operators, as demonstrated by the accompanying screenshots.