Cannot figure out how to save this field into database. You can consider adding a type converter for

一.场景：使用Room框架，报错，Cannot figure out how to save this field into database. You can consider adding a type converter for it。在ClassMomentInfo类中包含了两个成员变量，mMediaBeans和mClazzs，运行时候提示以上错误。错误代码如下： @Entity(tableName = "classMomentInfo") public class ClassMomentInfo { @PrimaryKey(autoGenerate=true) private long uid; //省略代码... //ROOM不支持直接存储集合 //@TypeConverters(MediaBeanTypeConverter.class) private List<MediaBean> mMediaBeans; //@TypeConverters(StringTypeConverter.class) private List<String> mClazzs; //省略代码... } 二.原因，Room不支持直接存储列表的功能三.解决方案3.1.新建类XxxConverter，代码如下： import android.arch.persistence.room.TypeConverter; import com.google.gson.Gson; import com.google.gson.reflect.TypeToken; import java.lang.reflect.Type; import java.util.Collections; import java.util.List; /** * describe:使用Room框架,room不支持对象中直接存储集合 * https://stackoverflow.com/questions/53812636/android-error-cannot-figure-out-how-to-save-this-field-into-database-you-can */ public class StringTypeConverter { Gson gson = new Gson(); @TypeConverter public List<String> stringToSomeObjectList(String data) { if (data == null) { return Collections.emptyList(); } Type listType = new TypeToken<List<String>>() {}.getType(); return gson.fromJson(data, listType); } @TypeConverter public String someObjectListToString(List<String> someObjects) { return gson.toJson(someObjects); } } 3.2.接着在ClassMomentInfo类中，在成员变量mClazzs上方添加"@TypeConverters(StringTypeConverter.class)";3.3.需要注意的是：在ClassMomentInfo类中，还有另外一个成员变量mMediaBeans，由于该成员变量存储的是MediaBean类型，所以需要单独创建类似StringTypeConverter的类，且需要在mMediaBeans上方加上“@TypeConverters(MediaBeanTypeConverter.class)”。此时，新建MediaBeanTypeConverter类，代码如下： import com.google.gson.Gson; import com.google.gson.reflect.TypeToken; import com.pj.teacherlocal.entity.work.MediaBean; import java.lang.reflect.Type; import java.util.Collections; import java.util.List; public class MediaBeanTypeConverter { Gson gson = new Gson(); @TypeConverter public List<MediaBean> stringToSomeObjectList(String data) { if (data == null) { return Collections.emptyList(); } Type listType = new TypeToken<List<MediaBean>>() {}.getType(); return gson.fromJson(data, listType); } @TypeConverter public String someObjectListToString(List<MediaBean> someObjects) { return gson.toJson(someObjects); } } 3.4.综上，处理方案已经很明显了。四.为了避免有些小伙伴疑惑，我将类ClassMomentInfo和类MediaBean的完整代码贴出来。

ClassMomentInfo

import android.arch.persistence.room.Embedded; import android.arch.persistence.room.Entity; import android.arch.persistence.room.PrimaryKey; import android.arch.persistence.room.TypeConverters; import com.pj.teacherlocal.entity.CurrentTeacherInfo; import com.pj.teacherlocal.utils.MediaBeanTypeConverter; import com.pj.teacherlocal.utils.StringTypeConverter; import java.util.List; @Entity(tableName = "classMomentInfo") public class ClassMomentInfo { @PrimaryKey(autoGenerate=true) private long uid; private String content; private String date; //ROOM不支持直接存储集合 @TypeConverters(MediaBeanTypeConverter.class) private List<MediaBean> mMediaBeans; @TypeConverters(StringTypeConverter.class) private List<String> mClazzs; //关联另外一个对象 @Embedded private CurrentTeacherInfo mCurrentTeacherInfo; public long getUid() { return uid; } public void setUid(long uid) { this.uid = uid; } public String getContent() { return content; } public void setContent(String content) { this.content = content; } public String getDate() { return date; } public void setDate(String date) { this.date = date; } public List<MediaBean> getMediaBeans() { return mMediaBeans; } public void setMediaBeans(List<MediaBean> mediaBeans) { mMediaBeans = mediaBeans; } public List<String> getClazzs() { return mClazzs; } public void setClazzs(List<String> clazzs) { mClazzs = clazzs; } public CurrentTeacherInfo getCurrentTeacherInfo() { return mCurrentTeacherInfo; } public void setCurrentTeacherInfo(CurrentTeacherInfo currentTeacherInfo) { mCurrentTeacherInfo = currentTeacherInfo; } @Override public String toString() { return "ClassMomentInfo{" + "uid=" + uid + ", content='" + content + '\'' + ", date='" + date + '\'' + ", mMediaBeans=" + mMediaBeans + ", mClazzs=" + mClazzs + ", mCurrentTeacherInfo=" + mCurrentTeacherInfo + '}'; } }

MediaBean

public class MediaBean { private String url; public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } @Override public String toString() { return "MediaBean{" + "url='" + url + '\'' + '}'; } }