在 QueryColumnBehavior 中新增静态字段 conditionCaster ，用于全局设置在满足一定条件后，将原条件转换为指定条件，例如将 column = null 转换为 column is null 。可兼容原有的 in 到 = 的智能转换。当智能转换被打开时，会先执行智能转换再执行 conditionCaster 的方法。

对应的测试方法在 DynamicConditionTest 中。

mybatis-flex-core/src/main/java/com/mybatisflex/core/query/QueryColumnBehavior.java

@@ -15,7 +15,12 @@
  */
 package com.mybatisflex.core.query;
 
+import com.mybatisflex.core.constant.SqlConsts;
+import com.mybatisflex.core.constant.SqlOperator;
+
+import java.util.Iterator;
 import java.util.Objects;
+import java.util.function.Function;
 import java.util.function.Predicate;
 
 /**
@@ -23,6 +28,7 @@ import java.util.function.Predicate;
  *
  * @author michael
  * @author 王帅
+ * @author CloudPlayer
  */
 public class QueryColumnBehavior {
 
@@ -36,11 +42,54 @@ public class QueryColumnBehavior {
     public static final Predicate<Object> IGNORE_EMPTY = o -> o == null || "".equals(o);
     public static final Predicate<Object> IGNORE_BLANK = o -> o == null || "".equals(o.toString().trim());
 
+    /**
+     * 在满足输入的数组或可迭代对象中的容量为 1 （即只有一个元素）时，自动将条件中的 in 转换为 =
+     */
+    public static final Function<? super QueryCondition, ? extends QueryCondition> CONVERT_IN_TO_EQUALS = it -> {
+        Object value = it.value;
+        if (value == null) {
+            return it;
+        }
+        if (it.logic.equalsIgnoreCase(SqlConsts.IN)) {
+            Object firstValue;
+            if (value instanceof Iterable<?>) {
+                Iterator<?> iter = ((Iterable<?>) value).iterator();
+                if (!iter.hasNext()) {  // 没有元素，直接返回原条件
+                    return it;
+                }
+                firstValue = iter.next();  // 取第一个元素
+                if (iter.hasNext()) {  // 如果有后续元素，则直接返回原条件
+                    return it;
+                }
+            } else if (value instanceof Object[]) {
+                Object[] array = (Object[]) value;
+                if (array.length != 1) {  // 如果不是单元素的数组就直接返回
+                    return it;
+                }
+                firstValue = array[0];  // 取第一个元素
+            } else {
+                return it;
+            }
+            return QueryCondition.create(it.column, SqlOperator.EQUALS, firstValue);  // 将 in 转换为 =
+        } else {
+            return it;
+        }
+    };
+
+    /**
+     * 如果使用了 = 来比较 null ，则将其转为 is null 。
+     */
+    public static final Function<? super QueryCondition, ? extends QueryCondition> CONVERT_EQUALS_TO_IS_NULL = it -> it.value == null ? it.column.isNull() : it;
     /**
      * 自定义全局的自动忽略参数的方法。
      */
     private static Predicate<Object> ignoreFunction = IGNORE_NULL;
 
+    /**
+     * 自定义全局的自动转换条件的方法。
+     */
+    private static Function<? super QueryCondition, ? extends QueryCondition> conditionCaster = Function.identity();
+
     /**
      * 当 {@code IN(...)} 条件只有 1 个参数时，是否自动把的内容转换为相等。
      */
@@ -66,4 +115,15 @@ public class QueryColumnBehavior {
         return ignoreFunction.test(value);
     }
 
+    public static Function<? super QueryCondition, ? extends QueryCondition> getConditionCaster() {
+        return smartConvertInToEquals ? CONVERT_IN_TO_EQUALS.andThen(conditionCaster) : conditionCaster;
+    }
+
+    public static void setConditionCaster(Function<? super QueryCondition, ? extends QueryCondition> conditionCaster) {
+        QueryColumnBehavior.conditionCaster = conditionCaster;
+    }
+
+    public static QueryCondition castCondition(QueryCondition condition) {
+        return getConditionCaster().apply(condition);
+    }
 }

mybatis-flex-core/src/test/java/com/mybatisflex/coretest/DynamicConditionTest.java

@@ -17,14 +17,19 @@
 package com.mybatisflex.coretest;
 
 import com.mybatisflex.core.constant.SqlConnector;
+import com.mybatisflex.core.constant.SqlOperator;
 import com.mybatisflex.core.query.*;
 import com.mybatisflex.core.util.StringUtil;
+import org.junit.Assert;
 import org.junit.Test;
 
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
 
+import static com.mybatisflex.core.query.QueryColumnBehavior.CONVERT_EQUALS_TO_IS_NULL;
+import static com.mybatisflex.core.query.QueryColumnBehavior.getConditionCaster;
 import static com.mybatisflex.core.query.QueryMethods.bracket;
 import static com.mybatisflex.core.query.QueryMethods.raw;
 import static com.mybatisflex.coretest.table.AccountTableDef.ACCOUNT;
@@ -227,4 +232,80 @@ public class DynamicConditionTest {
         System.out.println(qw.toSQL());
     }
 
+
+    private void assertConditionEquals(QueryCondition expect, QueryCondition actual) {
+        Assert.assertEquals(expect.getColumn(), actual.getColumn());
+        Assert.assertEquals(expect.getLogic(), actual.getLogic());
+        Assert.assertEquals(expect.getValue(), actual.getValue());
+    }
+
+    @Test
+    public void testCastFunction1() {
+        QueryCondition condition = QueryCondition.create(new QueryColumn("id"), SqlOperator.IN, new Object[] {null});
+        Assert.assertSame(condition, getConditionCaster().apply(condition));
+    }
+
+    @Test
+    public void testCastFunction2() {
+        QueryColumn column = new QueryColumn("id");
+        QueryColumnBehavior.setConditionCaster(CONVERT_EQUALS_TO_IS_NULL);
+
+        QueryCondition condition = QueryCondition.create(column, SqlOperator.EQUALS, null);
+        QueryCondition expect = column.isNull();
+        QueryCondition actual = getConditionCaster().apply(condition);
+
+        assertConditionEquals(expect, actual);
+    }
+
+    @Test
+    public void testCastFunction3() {
+        QueryColumn column = new QueryColumn("id");
+        QueryColumnBehavior.setConditionCaster(CONVERT_EQUALS_TO_IS_NULL);
+        QueryColumnBehavior.setSmartConvertInToEquals(true);
+
+        QueryCondition condition = QueryCondition.create(column, SqlOperator.EQUALS, null);
+        QueryCondition expect = column.isNull();
+        QueryCondition actual = getConditionCaster().apply(condition);
+
+        assertConditionEquals(expect, actual);
+    }
+
+    @Test
+    public void testCastFunction4() {
+        QueryColumn column = new QueryColumn("id");
+        QueryColumnBehavior.setConditionCaster(CONVERT_EQUALS_TO_IS_NULL);
+        QueryColumnBehavior.setSmartConvertInToEquals(true);
+
+        QueryCondition condition = QueryCondition.create(column, SqlOperator.IN, new Object[] { 1 });
+        QueryCondition expect = QueryCondition.create(column, SqlOperator.EQUALS, 1);
+        QueryCondition actual = getConditionCaster().apply(condition);
+
+        assertConditionEquals(expect, actual);
+    }
+
+    @Test
+    public void testCastFunction5() {
+        QueryColumn column = new QueryColumn("id");
+        QueryColumnBehavior.setConditionCaster(CONVERT_EQUALS_TO_IS_NULL);
+        QueryColumnBehavior.setSmartConvertInToEquals(true);
+
+        QueryCondition condition = QueryCondition.create(column, SqlOperator.IN, new Object[] { null });
+        QueryCondition expect = column.isNull();
+        QueryCondition actual = getConditionCaster().apply(condition);
+
+        assertConditionEquals(expect, actual);
+    }
+
+    @Test
+    public void testCastFunction6() {
+        QueryColumn column = new QueryColumn("id");
+        QueryColumnBehavior.setConditionCaster(CONVERT_EQUALS_TO_IS_NULL);
+        QueryColumnBehavior.setSmartConvertInToEquals(true);
+
+        QueryCondition condition = QueryCondition.create(column, SqlOperator.IN, Collections.singletonList(null));
+        QueryCondition expect = column.isNull();
+        QueryCondition actual = getConditionCaster().apply(condition);
+
+        assertConditionEquals(expect, actual);
+    }
 }