Mybatis动态元素if的使用方式
作者：三省同学
这篇文章主要介绍了Mybatis动态元素if的使用方式,具有很好的参考价值,希望对大家有所帮助,如有错误或未考虑完全的地方,望不吝赐教
问题
代码
<if test="status != null and status != ''">
AND status = #{status}
</if>
Mybatis动态元素if使用，上面写法适用于status类型为字符串。
若为整型，如int/Integer，当status为0时，就不会进入判断
解决
1：
<if test="status != null and status != '' or status == 0">
AND u.status = #{status}
</if>
2
<if test="status != null">
AND u.status = #{status}
</if>
源码阅读
查看SQL生成
根据断点进入PageInterceptor
@Override
public Object intercept(Invocation invocation) throws Throwable {
try {
Object[] args = invocation.getArgs();
MappedStatement ms = (MappedStatement) args[0];
Object parameter = args[1];
RowBounds rowBounds = (RowBounds) args[2];
ResultHandler resultHandler = (ResultHandler) args[3];
Executor executor = (Executor) invocation.getTarget();
CacheKey cacheKey;
BoundSql boundSql;
//由于逻辑关系，只会进入一次
if (args.length == 4) {
//4 个参数时
boundSql = ms.getBoundSql(parameter);
cacheKey = executor.createCacheKey(ms, parameter, rowBounds, boundSql);
} else {
//6 个参数时
cacheKey = (CacheKey) args[4];
boundSql = (BoundSql) args[5];
}
checkDialectExists();
//对 boundSql 的拦截处理
if (dialect instanceof BoundSqlInterceptor.Chain) {
boundSql = ((BoundSqlInterceptor.Chain) dialect).doBoundSql(BoundSqlInterceptor.Type.ORIGINAL, boundSql, cacheKey);
}
...
进入MappedStatement查看SQL动态绑定
public BoundSql getBoundSql(Object parameterObject) {
BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings == null || parameterMappings.isEmpty()) {
boundSql = new BoundSql(configuration, boundSql.getSql(), parameterMap.getParameterMappings(), parameterObject);
}
...
rootSqlNode.apply(context);这句代码很关键查看IF元素最终执行结果
@Override
public BoundSql getBoundSql(Object parameterObject) {
DynamicContext context = new DynamicContext(configuration, parameterObject);
rootSqlNode.apply(context);
SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
Class<?> parameterType = parameterObject == null ? Object.class : parameterObject.getClass();
SqlSource sqlSource = sqlSourceParser.parse(context.getSql(), parameterType, context.getBindings());
BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
for (Map.Entry<String, Object> entry : context.getBindings().entrySet()) {
boundSql.setAdditionalParameter(entry.getKey(), entry.getValue());
}
return boundSql;
}
循环动态元素节点
@Override
public boolean apply(DynamicContext context) {
for (SqlNode sqlNode : contents) {
sqlNode.apply(context);
}
return true;
}
进入类IfSqlNode
evaluator.evaluateBoolean(test, context.getBindings())如果为false就不会进入元素判断中
@Override
public boolean apply(DynamicContext context) {
if (evaluator.evaluateBoolean(test, context.getBindings())) {
contents.apply(context);
return true;
}
return false;
}
判断逻辑
public class ExpressionEvaluator {
public boolean evaluateBoolean(String expression, Object parameterObject) {
Object value = OgnlCache.getValue(expression, parameterObject);
if (value instanceof Boolean) {
return (Boolean) value;
}
if (value instanceof Number) {
return !new BigDecimal(String.valueOf(value)).equals(BigDecimal.ZERO);
}
return value != null;
}
...
进入类OgnlCache
public static Object getValue(String expression, Object root) {
try {
Map<Object, OgnlClassResolver> context = Ognl.createDefaultContext(root, new OgnlClassResolver());
return Ognl.getValue(parseExpression(expression), context, root);
} catch (OgnlException e) {
throw new BuilderException("Error evaluating expression '" + expression + "'. Cause: " + e, e);
}
}
protected Object evaluateGetValueBody(OgnlContext context, Object source) throws OgnlException {
context.setCurrentObject(source);
context.setCurrentNode(this);
if (!this._constantValueCalculated) {
this._constantValueCalculated = true;
boolean constant = this.isConstant(context);
if (constant) {
this._constantValue = this.getValueBody(context, source);
}
this._hasConstantValue = constant;
}
return this._hasConstantValue ? this._constantValue : this.getValueBody(context, source);
}
protected Object getValueBody(OgnlContext context, Object source) throws OgnlException {
Object v1 = this._children[0].getValue(context, source);
Object v2 = this._children[1].getValue(context, source);
return OgnlOps.equal(v1, v2) ? Boolean.FALSE : Boolean.TRUE;
}
public static boolean equal(Object v1, Object v2) {
if (v1 == null) {
return v2 == null;
} else if (v1 != v2 && !isEqual(v1, v2)) {
if (v1 instanceof Number && v2 instanceof Number) {
return ((Number)v1).doubleValue() == ((Number)v2).doubleValue();
} else {
return false;
}
} else {
return true;
}
}
public static boolean isEqual(Object object1, Object object2) {
boolean result = false;
if (object1 == object2) {
result = true;
} else if (object1 != null && object1.getClass().isArray()) {
if (object2 != null && object2.getClass().isArray() && object2.getClass() == object1.getClass()) {
result = Array.getLength(object1) == Array.getLength(object2);
if (result) {
int i = 0;
for(int icount = Array.getLength(object1); result && i < icount; ++i) {
result = isEqual(Array.get(object1, i), Array.get(object2, i));
}
}
}
} else {
result = object1 != null && object2 != null && (object1.equals(object2) || compareWithConversion(object1, object2) == 0);
}
return result;
}
关键代码
public static int compareWithConversion(Object v1, Object v2) {
int result;
if (v1 == v2) {
result = 0;
} else {
int t1 = getNumericType(v1);
int t2 = getNumericType(v2);
int type = getNumericType(t1, t2, true);
switch(type) {
case 6:
result = bigIntValue(v1).compareTo(bigIntValue(v2));
break;
case 9:
result = bigDecValue(v1).compareTo(bigDecValue(v2));
break;
case 10:
if (t1 == 10 && t2 == 10) {
if (v1 instanceof Comparable && v1.getClass().isAssignableFrom(v2.getClass())) {
result = ((Comparable)v1).compareTo(v2);
break;
}
throw new IllegalArgumentException("invalid comparison: " + v1.getClass().getName() + " and " + v2.getClass().getName());
}
case 7:
case 8:
double dv1 = doubleValue(v1);
double dv2 = doubleValue(v2);
return dv1 == dv2 ? 0 : (dv1 < dv2 ? -1 : 1);
default:
long lv1 = longValue(v1);
long lv2 = longValue(v2);
return lv1 == lv2 ? 0 : (lv1 < lv2 ? -1 : 1);
}
}
return result;
}
public static double doubleValue(Object value) throws NumberFormatException {
if (value == null) {
return 0.0D;
} else {
Class c = value.getClass();
if (c.getSuperclass() == Number.class) {
return ((Number)value).doubleValue();
} else if (c == Boolean.class) {
return (Boolean)value ? 1.0D : 0.0D;
} else if (c == Character.class) {
return (double)(Character)value;
} else {
// 原因就这了！！！
String s = stringValue(value, true);
return s.length() == 0 ? 0.0D : Double.parseDouble(s);
}
}
}
为什么为0时，进不去
结论：
从断点跟进源码得出，当！=null条件是，Mybatis会把传进去的值与null比较，0.0==null为false，当比较空字符""时，会先把空字符进行一次转化doubleValue(v2)，结果为0.0。
所以当status是整型且为0时，就不会进入判断
重要源码节点
SimpleNode::getValue—>SimpleNode::evaluateGetValueBody—>ASTEq::getValueBody—>OgnlOps::equal—>OgnlOps::compareWithConversion
总结
以上为个人经验，希望能给大家一个参考，也希望大家多多支持脚本之家。