我使用Rails-React运行它以从数据库（mongoDB）返回数据。已成功连接数据库。但是，它返回错误“TypeError：home_fires is undefined”，请帮助...
03-16 09:50:30.987 11672-11672/com.example.tanmay.shoppingapp E/SQLiteLog: (1) table cart has no column named _id
03-16 09:50:30.991 11672-11672/com.example.tanmay.shoppingapp E/SQLiteDatabase: Error inserting quantity=37 _id=2
android.database.sqlite.SQLiteException: table cart has no column named _id (code 1): , while compiling: INSERT INTO cart(quantity,_id) VALUES (?,?)
at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:889)
at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:500)
at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
at android.database.sqlite.SQLiteStatement.<init>(SQLiteStatement.java:31)
at android.database.sqlite.SQLiteDatabase.insertWithOnConflict(SQLiteDatabase.java:1472)
at android.database.sqlite.SQLiteDatabase.insert(SQLiteDatabase.java:1343)
at com.example.tanmay.shoppingapp.DataSet.DataProvider.insertCart(DataProvider.java:169)
at com.example.tanmay.shoppingapp.DataSet.DataProvider.insert(DataProvider.java:155)
at android.content.ContentProvider$Transport.insert(ContentProvider.java:264)
at android.content.ContentResolver.insert(ContentResolver.java:1279)
at com.example.tanmay.shoppingapp.YourCart.onCreate(YourCart.java:34)
at android.app.Activity.performCreate(Activity.java:6684)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2652)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2766)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1507)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6236)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:891)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:781)
03-16 09:50:30.991 11672-11672/com.example.tanmay.shoppingapp E/com.whatever.tag: Failed to insert row for content://com.example.tanmay.shoppingapp/cart
03-16 09:50:30.992 11672-11672/com.example.tanmay.shoppingapp E/SQLiteLog: (1) no such column: _id
03-16 09:50:30.994 11672-11672/com.example.tanmay.shoppingapp D/AndroidRuntime: Shutting down VM
03-16 09:50:30.996 11672-11672/com.example.tanmay.shoppingapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.tanmay.shoppingapp, PID: 11672
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.tanmay.shoppingapp/com.example.tanmay.shoppingapp.YourCart}: android.database.sqlite.SQLiteException: no such column: _id (code 1): , while compiling: SELECT _id, quantity FROM cart
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2699)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2766)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1507)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6236)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:891)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:781)
Caused by: android.database.sqlite.SQLiteException: no such column: _id (code 1): , while compiling: SELECT _id, quantity FROM cart
at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:889)
at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:500)
at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1318)
at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1165)
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1036)
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1204)
at com.example.tanmay.shoppingapp.DataSet.DataProvider.query(DataProvider.java:92)
at android.content.ContentProvider.query(ContentProvider.java:1020)
at android.content.ContentProvider$Transport.query(ContentProvider.java:239)
at android.content.ContentResolver.query(ContentResolver.java:534)
at android.content.ContentResolver.query(ContentResolver.java:475)
at com.example.tanmay.shoppingapp.YourCart.onCreate(YourCart.java:44)
at android.app.Activity.performCreate(Activity.java:6684)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2652)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2766)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1507)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6236)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:891)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:781)
以下是我呈现数据的方式constructor(props) {
super(props);
let home_fires = type.string;
this.state = {
error: null,
isLoaded: false,
home_fires: []
};
}
componentDidMount() {
fetch("http://localhost:3000/api/home_fires")
.then(res => res.json())
.then(
(results) => {
this.setState({
isLoaded: true,
home_fires: results.home_fires
});
},
(error) => {
this.setState({
isLoaded: true,
error
});
}
)
}
答案 0 :(得分：0)
我认为你的地图功能应该像
randomColor({ luminosity: 'light', hue: 'blue' });
另外，如果你在同一个组件中调用home_fires，它应该是，
this.props.home_fires.map(home_fire => <div>{home_fire.bla}</div>)
答案 1 :(得分：0)
我认为这是因为构造函数，只需删除
让home_fires = type.string;