房间数据库迁移：java.lang.IllegalStateException:迁移没有'；t正确处理<；表_name>；

我正在尝试使用Room数据库创建一个新表。我遵循的原则与我在程序中已有的第一个表相同，但当运行应用程序时，我会出现以下错误：

Caused by: java.lang.IllegalStateException: Migration didn't properly handle: WaterFountainEntry(com.mpms.relatorioacessibilidadecortec.entities.WaterFountainEntry).
     Expected:
    TableInfo{name='WaterFountainEntry', columns={waterFountainHeight=Column{name='waterFountainHeight', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}, waterFountainID=Column{name='waterFountainID', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=1, defaultValue='null'}, cupHolderHeight=Column{name='cupHolderHeight', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}, schoolEntryID=Column{name='schoolEntryID', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=0, defaultValue='null'}, waterFountApproximation=Column{name='waterFountApproximation', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}}, foreignKeys=[ForeignKey{referenceTable='SchoolEntry', onDelete='CASCADE', onUpdate='CASCADE', columnNames=[schoolEntryID], referenceColumnNames=[cadID]}], indices=[]}
     Found:
    TableInfo{name='WaterFountainEntry', columns={waterFountainID=Column{name='waterFountainID', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1, defaultValue='null'}, waterFountainHeight=Column{name='waterFountainHeight', type='DOUBLE', affinity='4', notNull=true, primaryKeyPosition=0, defaultValue='null'}, cupHolderHeight=Column{name='cupHolderHeight', type='DOUBLE', affinity='4', notNull=true, primaryKeyPosition=0, defaultValue='null'}, schoolEntryID=Column{name='schoolEntryID', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0, defaultValue='null'}, waterFountApproximation=Column{name='waterFountApproximation', type='DOUBLE', affinity='4', notNull=true, primaryKeyPosition=0, defaultValue='null'}}, foreignKeys=[ForeignKey{referenceTable='SchoolEntry', onDelete='NO ACTION', onUpdate='NO ACTION', columnNames=[schoolEntryID], referenceColumnNames=[cadID]}], indices=[]}

通过阅读此错误消息，我确实收集到程序希望某些字段的类型不同（可能顺序也不同），但问题是它不应该是这样的。我确保完全按照我在实体中放置字段的方式编写迁移类，如下所示：

---

那么，错误是什么呢？我真的读了很多文档，找不到这个问题的原因。

绿色栏就是迁移的样子

请检查突出显示的字段，并进行类似于绿色的更改，因为这是您的预期结果

这里是到的链接以供比较

只需比较发现的结果和预期结果，您就会知道在迁移过程中需要做哪些更改

 Expected:
    TableInfo{name='WaterFountainEntry', columns={waterFountainHeight=Column{name='waterFountainHeight', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}, waterFountainID=Column{name='waterFountainID', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=1, defaultValue='null'}, cupHolderHeight=Column{name='cupHolderHeight', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}, schoolEntryID=Column{name='schoolEntryID', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=0, defaultValue='null'}, waterFountApproximation=Column{name='waterFountApproximation', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}}, foreignKeys=[ForeignKey{referenceTable='SchoolEntry', onDelete='CASCADE', onUpdate='CASCADE', columnNames=[schoolEntryID], referenceColumnNames=[cadID]}], indices=[]}
     Found:
    TableInfo{name='WaterFountainEntry', columns={waterFountainID=Column{name='waterFountainID', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1, defaultValue='null'}, waterFountainHeight=Column{name='waterFountainHeight', type='DOUBLE', affinity='4', notNull=true, primaryKeyPosition=0, defaultValue='null'}, cupHolderHeight=Column{name='cupHolderHeight', type='DOUBLE', affinity='4', notNull=true, primaryKeyPosition=0, defaultValue='null'}, schoolEntryID=Column{name='schoolEntryID', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0, defaultValue='null'}, waterFountApproximation=Column{name='waterFountApproximation', type='DOUBLE', affinity='4', notNull=true, primaryKeyPosition=0, defaultValue='null'}}, foreignKeys=[ForeignKey{referenceTable='SchoolEntry', onDelete='NO ACTION', onUpdate='NO ACTION', columnNames=[schoolEntryID], referenceColumnNames=[cadID]}], indices=[]}

---

预期和找到的SQL脚本之间存在许多差异；以

cupHolderHeight

列为例：

杯托重量栏：

• 预期：

  REAL

  找到：

  DOUBLE

  -->将其更改为REAL（基本上是 SQLite中没有

  DOUBLE

  类型）
• 预期为

  notNull=false

  ，发现为

  notNull=true

  -->将其更改为false（即NULL）

将其应用于迁移SQL脚本：

将

cupHolderHeight DOUBLE NOT NULL

更改为

cupHolderHeight REAL

您需要浏览其他列并执行相同的操作。最终，脚本应该是这样的：

database.execSQL("CREATE TABLE WaterFountainEntry (waterFountainID INTEGER PRIMARY KEY AUTOINCREMENT," +
                    "schoolEntryID INTEGER, waterFountainHeight REAL, cupHolderHeight REAL," +
                    "waterFountApproximation REAL, FOREIGN KEY (schoolEntryID) REFERENCES SchoolEntry (cadID) ON UPDATE CASCADE ON DELETE CASCADE)");

<>你也可以考虑更多的说明。

用于安排和比较找到的脚本和预期脚本：

您可以使用编程脚本对它们进行排序，但以下是使用一些工具对它们进行排序的方法：

将第一个（预期）复制到文本编辑器中：

将

}，

替换为

}，\n

-->您必须知道如何在文本编辑器中添加换行符：

现在，您将把每一列放在一个单独的行中：

对另一个（找到的）执行1和2：

现在很容易按字母顺序对它们进行排序，并将一个值与另一个值进行比较（Excel可以作为一种工具）

---

获取正确SQL的简单技巧是让Room代表您生成SQL

创建实体，然后编译（Cntrl+F9），然后查看生成的java（从Android视图），然后查找与@Database类相同并带有_Impl后缀的文件，然后找到createAllTables方法，SQL就在那里。这正是房间所期望的

e、 g:-

---

如果您先按相同的顺序重新排列列，您将获得更好的差异（Room不关心顺序），那么，我如何重新排列列？我在研究时找不到任何类似的东西。如果你看图片，列的顺序是不同的。在第一幅图像中，WaterCountainId是第一列，但在第二幅图像中，WaterCountainHeight是第一列。如果可以对它们进行重新排序，则比较差异会很容易。重新排序错误文本与代码无关。@CorMatt我已为您更新了图像如果我直接从实体创建表，则无法在创建实体时使用“真实”值。将

Double

更改为

Real

不会在迁移类中产生任何问题？您可以在entity中正常使用

Double

，Room database将在

Real

和

Double

之间来回转换，但在

database.execSQL（）

中需要编写SQL脚本而不是java脚本

 Expected:
    TableInfo{name='WaterFountainEntry', columns={waterFountainHeight=Column{name='waterFountainHeight', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}, waterFountainID=Column{name='waterFountainID', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=1, defaultValue='null'}, cupHolderHeight=Column{name='cupHolderHeight', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}, schoolEntryID=Column{name='schoolEntryID', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=0, defaultValue='null'}, waterFountApproximation=Column{name='waterFountApproximation', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}}, foreignKeys=[ForeignKey{referenceTable='SchoolEntry', onDelete='CASCADE', onUpdate='CASCADE', columnNames=[schoolEntryID], referenceColumnNames=[cadID]}], indices=[]}
     Found:
    TableInfo{name='WaterFountainEntry', columns={waterFountainID=Column{name='waterFountainID', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1, defaultValue='null'}, waterFountainHeight=Column{name='waterFountainHeight', type='DOUBLE', affinity='4', notNull=true, primaryKeyPosition=0, defaultValue='null'}, cupHolderHeight=Column{name='cupHolderHeight', type='DOUBLE', affinity='4', notNull=true, primaryKeyPosition=0, defaultValue='null'}, schoolEntryID=Column{name='schoolEntryID', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0, defaultValue='null'}, waterFountApproximation=Column{name='waterFountApproximation', type='DOUBLE', affinity='4', notNull=true, primaryKeyPosition=0, defaultValue='null'}}, foreignKeys=[ForeignKey{referenceTable='SchoolEntry', onDelete='NO ACTION', onUpdate='NO ACTION', columnNames=[schoolEntryID], referenceColumnNames=[cadID]}], indices=[]}

database.execSQL("CREATE TABLE WaterFountainEntry (waterFountainID INTEGER PRIMARY KEY AUTOINCREMENT," +
                    "schoolEntryID INTEGER, waterFountainHeight REAL, cupHolderHeight REAL," +
                    "waterFountApproximation REAL, FOREIGN KEY (schoolEntryID) REFERENCES SchoolEntry (cadID) ON UPDATE CASCADE ON DELETE CASCADE)");

TableInfo{name='WaterFountainEntry', columns={waterFountainHeight=Column{name='waterFountainHeight', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}, waterFountainID=Column{name='waterFountainID', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=1, defaultValue='null'}, cupHolderHeight=Column{name='cupHolderHeight', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}, schoolEntryID=Column{name='schoolEntryID', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=0, defaultValue='null'}, waterFountApproximation=Column{name='waterFountApproximation', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}}, foreignKeys=[ForeignKey{referenceTable='SchoolEntry', onDelete='CASCADE', onUpdate='CASCADE', columnNames=[schoolEntryID], referenceColumnNames=[cadID]}], indices=[]}

TableInfo{name='WaterFountainEntry', columns={waterFountainHeight=Column{name='waterFountainHeight', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'},
waterFountainID=Column{name='waterFountainID', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=1, defaultValue='null'},
cupHolderHeight=Column{name='cupHolderHeight', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'},
schoolEntryID=Column{name='schoolEntryID', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=0, defaultValue='null'},
waterFountApproximation=Column{name='waterFountApproximation', type='REAL', affinity='4', notNull=false, primaryKeyPosition=0, defaultValue='null'}},
foreignKeys=[ForeignKey{referenceTable='SchoolEntry', onDelete='CASCADE', onUpdate='CASCADE', columnNames=[schoolEntryID], referenceColumnNames=[cadID]}], indices=[]}

TableInfo{name='WaterFountainEntry', columns={waterFountainID=Column{name='waterFountainID', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1, defaultValue='null'},
waterFountainHeight=Column{name='waterFountainHeight', type='DOUBLE', affinity='4', notNull=true, primaryKeyPosition=0, defaultValue='null'},
cupHolderHeight=Column{name='cupHolderHeight', type='DOUBLE', affinity='4', notNull=true, primaryKeyPosition=0, defaultValue='null'},
schoolEntryID=Column{name='schoolEntryID', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0, defaultValue='null'},
waterFountApproximation=Column{name='waterFountApproximation', type='DOUBLE', affinity='4', notNull=true, primaryKeyPosition=0, defaultValue='null'}},
foreignKeys=[ForeignKey{referenceTable='SchoolEntry', onDelete='NO ACTION', onUpdate='NO ACTION', columnNames=[schoolEntryID], referenceColumnNames=[cadID]}], indices=[]}