How can use firestore using where and orderby in flutter? - firebase

Question

How can use firestore using where and orderby in flutter?
When I wanna to use both, I got the error.
Exception has occurred.
_CastError (Null check operator used on a null value)
code
StreamBuilder(
stream: FirebaseFirestore.instance
.collection('Posts')
.where('country', isEqualTo: user.country)
//.where('country', isEqualTo: 'Australia')
.orderBy('time', descending: true)
.snapshots(),
builder: (context,
AsyncSnapshot<QuerySnapshot<Map<String, dynamic>>> snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return const Center(
child: CircularProgressIndicator(),
);
}
//print(user.country);
return ListView.builder(
itemCount: snapshot.data!.docs.length,
itemBuilder: (context, index) => Container(
margin: EdgeInsets.symmetric(
horizontal: width > webScreenSize ? width * 0.3 : 0,
vertical: width > webScreenSize ? 15 : 0),
child: PostCard(
snap: snapshot.data!.docs[index],
),
),
);
},
So, why I could not got the data? I'd got the user.value.

Answer 1

The problem is that you're telling Flutter that snapshot.data is guaranteed to have a value, when in reality it doesn't here:
return ListView.builder(
itemCount: snapshot.data!.docs.length,
I recommend reading the documentation for StreamBuilder again, as there are many more states than snapshot.connectionState == ConnectionState.waiting that you need to handle.
For example, there could be an error, or there could be no data for another reason:
StreamBuilder(
stream: FirebaseFirestore.instance
.collection('Posts')
.where('country', isEqualTo: user.country)
.orderBy('time', descending: true)
.snapshots(),
builder: (context, AsyncSnapshot<QuerySnapshot<Map<String, dynamic>>> snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return const Center(
child: CircularProgressIndicator(),
);
}
// 👇 Handle error
if (snapshot.hasError) {
return const Center(
child: Text(snapshot.error),
);
}
// 👇 Handle lack of data
if (!snapshot.hasData) {
return const Center(
child: Text("Something when wrong - no data available"),
);
}
return ListView.builder(
itemCount: snapshot.data!.docs.length,
itemBuilder: (context, index) => Container(
margin: EdgeInsets.symmetric(
horizontal: width > webScreenSize ? width * 0.3 : 0,
vertical: width > webScreenSize ? 15 : 0),
child: PostCard(
snap: snapshot.data!.docs[index],
),
),
);