集成 mybatisplus-plus时，联合主键中带“id”字段报错问题

问题描述

当集成mybatisplus-plus

<dependency>
  <groupId>com.github.jeffreyning</groupId>
  <artifactId>mybatisplus-plus</artifactId>
  <version>1.5.1-RELEASE</version>
</dependency>
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且联合主键中有一个字段名称为“id”时

@MppMultiId
@TableField
private String id;
@MppMultiId
@TableField
private String roleId;
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调用selectByMultiId方法时会报错：

java.lang.RuntimeException: not found column for id
com.github.jeffreyning.mybatisplus.base.SelectByMultiIdMethod.getCol(SelectByMultiIdMethod.java:32)
com.github.jeffreyning.mybatisplus.base.SelectByMultiIdMethod.createWhere(SelectByMultiIdMethod.java:42)
com.github.jeffreyning.mybatisplus.base.SelectByMultiIdMethod.injectMappedStatement(SelectByMultiIdMethod.java:64)
com.baomidou.mybatisplus.core.injector.AbstractMethod.inject(AbstractMethod.java:67)
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原因分析

1. 当实体类没有设置“TableId”注解时,TableInfoHelper类在构造TableInfo时会自动将属性名称为“id”的字段设置为主键字段，不会添加到TableInfo的fieldList中

//com/baomidou/mybatisplus/core/metadata/TableInfoHelper.class
private static boolean initTableIdWithoutAnnotation(DbConfig dbConfig, TableInfo tableInfo, Field field) {
        String property = field.getName();
        if ("id".equalsIgnoreCase(property)) {  // 对id字段做特殊处理
            if (field.getAnnotation(TableField.class) != null) {
                logger.warn(String.format("This \"%s\" is the table primary key by default name for `id` in Class: \"%s\",So @TableField will not work!", property, tableInfo.getEntityType().getName()));
            }

            String column = property;
            if (dbConfig.isCapitalMode()) {
                column = property.toUpperCase();
            }

            Class<?> keyType = tableInfo.getReflector().getGetterType(property);
            if (keyType.isPrimitive()) {
                logger.warn(String.format("This primary key of \"%s\" is primitive !不建议如此请使用包装类 in Class: \"%s\"", property, tableInfo.getEntityType().getName()));
            }

            tableInfo.setKeyRelated(checkRelated(tableInfo.isUnderCamel(), property, column)).setIdType(dbConfig.getIdType()).setKeyColumn(column).setKeyProperty(property).setKeyType(keyType);
            return true;
        } else {
            return false;
        }
    }
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2. 再SelectByMultiIdMethod的处理中，会从FieldList中查字段信息，自然就查询到不到id字段，所以就会报错

// com/github/jeffreyning/mybatisplus/base/SelectByMultiIdMethod
private String createWhere(Class<?> modelClass, TableInfo tableInfo) {
        List<TableFieldInfo> fieldList = tableInfo.getFieldList();
        Field[] fieldArray = modelClass.getDeclaredFields();
        Map<String, String> idMap = new HashMap();
        Field[] var6 = fieldArray;
        int var7 = fieldArray.length;

        for(int var8 = 0; var8 < var7; ++var8) {
            Field field = var6[var8];
            MppMultiId mppMultiId = (MppMultiId)field.getAnnotation(MppMultiId.class);
            if (mppMultiId != null) {
                String attrName = field.getName();
                String colName = this.getCol(fieldList, attrName); // 从FieldList中查字段
                idMap.put(attrName, colName);
            }
        }

        if (idMap.isEmpty()) {
            logger.info("entity {} not contain MppMultiId anno", modelClass.getName());
            return null;
        } else {
            StringBuilder sb = new StringBuilder("");
            idMap.forEach((attrNamex, colNamex) -> {
                if (sb.length() > 0) {
                    sb.append(" and ");
                }

                sb.append(colNamex).append("=").append("#{").append(attrNamex).append("}");
            });
            return sb.toString();
        }
    }
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解决方案

方案1：实体类的联合主键字段不要使用“Id”，换成其他的

@MppMultiId
@TableField("id") // 属性名换掉，指定数据表列名
private String userId;
@MppMultiId
@TableField
private String roleId;
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方案2：在无法修改实体类（实例类自动生成出来的）情况下则需要重写TableInfoHelper类，考虑MppMultiId的情况：

​ 属性名称为“id” 且没有MppMultiId注解 且 实体类上没有TableId注解 ，才将id设置为主键 .

private static boolean initTableIdWithoutAnnotation(DbConfig dbConfig, TableInfo tableInfo, Field field) {
  String property = field.getName();
  // 属性名称为“id” 且没有MppMultiId注解  且 实体类上没有TableId注解 ，才将id设置为主键 .
  if ("id".equalsIgnoreCase(property) && field.getAnnotation(MppMultiId.class) == null) {
    if (field.getAnnotation(TableField.class) != null) {
      logger.warn(String.format("This \"%s\" is the table primary key by default name for `id` in Class: \"%s\",So @TableField will not work!", property, tableInfo.getEntityType().getName()));
    }

    String column = property;
    if (dbConfig.isCapitalMode()) {
      column = property.toUpperCase();
    }

    Class<?> keyType = tableInfo.getReflector().getGetterType(property);
    if (keyType.isPrimitive()) {
      logger.warn(String.format("This primary key of \"%s\" is primitive !不建议如此请使用包装类 in Class: \"%s\"", property, tableInfo.getEntityType().getName()));
    }

    tableInfo.setKeyRelated(checkRelated(tableInfo.isUnderCamel(), property, column)).setIdType(dbConfig.getIdType()).setKeyColumn(column).setKeyProperty(property).setKeyType(keyType);
    return true;
  } else {
    return false;
  }
}
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