java– 如何读取firestore子集合并将其传递给FirestoreRecyclerOptions

概述I有root产品的firestore数据库,每个产品都有集合’comments’,所以我存储了所有用户对这个产品的评论,但是当对这个评论子集合的查询时,我从firestore获得空值或零快照privatevoidgetCommentObject(){query=FirebaseFirestore.getInstance().collect

I有root产品的firestore数据库,每个产品都有集合’comments’,所以我存储了所有用户对这个产品的评论,但是当对这个评论子集合的查询时,我从firestore获得空值或零快照

   private voID getCommentObject(){    query = FirebaseFirestore.getInstance()            .collection("products").document(docID).collection("comments");    FirestoreRecyclerOptions<CommentModel> options = new FirestoreRecyclerOptions.Builder<CommentModel>()            .setquery(query, CommentModel.class)            .build();    adapter = new FirestoreRecyclerAdapter<CommentModel, commentHolder>(options) {        @NonNull        @OverrIDe        public commentHolder onCreateVIEwHolder(@NonNull VIEwGroup parent, int vIEwType) {            VIEw vIEw = LayoutInflater.from(parent.getContext())                    .inflate(R.layout.comment_item_layout, parent, false);            return new commentHolder(vIEw);        }        @OverrIDe        protected voID onBindVIEwHolder(@NonNull commentHolder commentHolder, int position, @NonNull CommentModel commentModel) {            commentHolder.full_comment.setText(String.valueOf(commentModel.getComment()));            commentHolder.comment_date.setText(String.valueOf(commentModel.getCommentDate()));            commentHolder.comment_user.setText(String.valueOf(commentModel.getCommentUser()));            GlIDe.with(getApplicationContext())                    .load(commentModel.getProfilePic())                    .into(commentHolder.userProfileimg);        };    };    rv.setAdapter(adapter);    adapter.notifyDataSetChanged();}

这是我的评论模型

@IgnoreExtraPropertIEs

公共类CommentModel实现Serializable {

public CommentModel() {}String comment ,  commentDate , profilePic , commentUser ;public CommentModel(String comment) {    this.comment = comment;}public String getComment() {    return this.comment;}public voID setComment(String Comment) {    this.comment = comment;}public String getCommentDate() {    return this.commentDate;}public voID setCommentDate(String commentDate) {    commentDate = commentDate;}public String getProfilePic() {    return profilePic;}public voID setProfilePic(String profilePic) {    this.profilePic = profilePic;}public String getCommentUser() {    return commentUser;}public voID setCommentUser(String commentUser) {    commentUser = commentUser;}

}

解决方法:

代码中的问题在于,CommentModel类中的字段名称与数据库中属性的名称不同.您在CommentModel类中有一个名为comment的字段,但在您的数据库中我将​​其视为Comment,这是不正确的.名称必须匹配.当您使用名为getComment()的getter时,Firebase会在数据库中查找名为comment而不是Comment的字段.请参阅小写字母c对大写字母C？

有两种方法可以解决此问题.第一个是通过根据Java Naming Conventions重命名字段来更改模型类.因此,模型类应如下所示：

public class CommentModel {    private String comment, commentDate, profilePic, commentUser;    public CommentModel() {}    public CommentModel(String comment, String commentDate, String profilePic, String commentUser) {        this.comment = comment;        this.commentDate = commentDate;        this.profilePic = profilePic;        this.commentUser = commentUser;    }    public String getComment() { return comment; }    public String getCommentDate() { return commentDate; }    public String getProfilePic() { return profilePic; }    public String getCommentUser() { return commentUser; }}

在此示例中,您可以看到私有字段和公共getter.还有一个更简单的解决方案,直接在公共字段上设置值,如下所示：

public class CommentModel {    public String comment, commentDate, profilePic, commentUser;}

现在只需删除当前数据并使用正确的名称再次添加.只有在您处于测试阶段时,此解决方案才有效.

还有第二种方法,即使用注释.因此,如果您更喜欢使用私有字段和公共getter,则应仅在getter前面使用PropertyName注释.所以你的CommentModel类应该如下所示：

public class CommentModel {    private String comment, commentDate, profilePic, commentUser;    public CommentModel() {}    public CommentModel(String comment, String commentDate, String profilePic, String commentUser) {        this.comment = comment;        this.commentDate = commentDate;        this.profilePic = profilePic;        this.commentUser = commentUser;    }    @Propertyname("Comment")    public String getComment() { return comment; }    @Propertyname("CommentDate")    public String getCommentDate() { return commentDate; }    @Propertyname("ProfilePic")    public String getProfilePic() { return profilePic; }    @Propertyname("CommentUser")    public String getCommentUser() { return commentUser; }}

不要忘记开始倾听变化.

附：在你的课堂上,它应该是：

this.commentDate = commentDate;

并不是：

commentDate = commentDate;

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