CODEWITHSUNDEEP
javaandroidandroid-room
Tushar Gogna
Tushar Gogna

Reputation: 5083

Android Room Database: How to handle Arraylist in an Entity?

I just implemented Room for offline data saving. But in an Entity class, I am getting the following error:

Error:(27, 30) error: Cannot figure out how to save this field into database. You can consider adding a type converter for it.

And the class is as following:

@Entity(tableName = "firstPageData")
public class MainActivityData {

    @PrimaryKey
    private String userId;

    @ColumnInfo(name = "item1_id")
    private String itemOneId;

    @ColumnInfo(name = "item2_id")
    private String itemTwoId;

    // THIS IS CAUSING THE ERROR... BASICALLY IT ISN'T READING ARRAYS
    @ColumnInfo(name = "mylist_array")
    private ArrayList<MyListItems> myListItems;

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public ArrayList<MyListItems> getMyListItems() {
        return myListItems;
    }

    public void setCheckListItems(ArrayList<MyListItems> myListItems) {
        this.myListItems = myListItems;
    }

}

So basically I want to save the ArrayList in the database but I was not able to find anything relevant to it. Can you guide me regarding how to save an Array using Room?

NOTE: MyListItems Pojo class contains 2 Strings (as of now)

Upvotes: 151

Views: 160896

Answers (20)

Anna M
Anna M

Reputation: 63

If you only want to save and retrieve String list, then I think there is no need for JSON serialization.

Using built-in functions are much simpler and you can avoid reflection too.

Kotlin code:

class Converter {

    @TypeConverter
    fun List<String>.toStringData() = this.joinToString(STRING_SEPARATOR)

    @TypeConverter
    fun String.toList() = this.split(STRING_SEPARATOR)
}

Java code:

public class Converter {

    @TypeConverter
    public static String[] toArray(String data) {
        return data.split(STRING_SEPARATOR);
    }

    @TypeConverter
    public static String toString(String[] data) {
        return String.join(STRING_SEPARATOR, data);
    }
}

Upvotes: 3

jagadishlakkurcom jagadishlakk
jagadishlakkurcom jagadishlakk

Reputation: 597

When we are using TypeConverters then datatype should be return type of TypeConverter method.

For example: TypeConverter method returns a string, then adding table column should be of type string.

private static final Migration MIGRATION_1_2 = new Migration(1, 2) {
    @Override
    public void migrate(@NonNull SupportSQLiteDatabase database) {
        // Since we didn't alter the table, there's nothing else to do here.
        database.execSQL("ALTER TABLE "+  Collection.TABLE_STATUS  + " ADD COLUMN deviceType TEXT;");
        database.execSQL("ALTER TABLE "+  Collection.TABLE_STATUS  + " ADD COLUMN inboxType TEXT;");
    }
};

Upvotes: 1

M&#233;lanie Marliacy
M&#233;lanie Marliacy

Reputation: 1

I wanted to store a List containing photos URI in ROOM database . Because of special characters I was getting this error localized in my converter class, TypeConverters.class:

com.google.gson.stream.MalformedJsonException: Unterminated array at line 1 column 8 path $[1]

There was a problem in my simple converter for arrayList of String, in fact it was :

public static List<String> fromString(String value) {
    Type listType = new TypeToken<ArrayList<String>>() {
    }.getType();
    return new Gson().fromJson(value, listType);
}

@TypeConverter
public static String fromArrayList(List<String> list) {
    Gson gson = new Gson();
    return gson.toJson(list);
}

By taking @Derrick Njeru comment back, I changed it for that it could take in consideration a String as "https://images.app.goo.gl/jwhkhzhZVWrceQV67" like this :

    @TypeConverter
public List<String> gettingListFromString(String genreIds) {
    List<String> list = new ArrayList<>();

    String[] array = genreIds.split(",");
    
    for (String s : array) {
        if (!s.isEmpty()) {
            list.add(s);
        }
    }
    return list;
}

@TypeConverter
public String writingStringFromList(List<String> list) {
    String genreIds = "";
    for (String i : list) {
        genreIds += "," + i;
    }
    return genreIds;
}

Upvotes: -1

canerkaseler
canerkaseler

Reputation: 7468

Kotlin Answer

You need to do 3 things:

  1. Create Converters class.
  2. Add Converters class on Database.
  3. Just define what you want to use in Entity class.

Usage example step by step:

Step 1 :

 class Converters {

    @TypeConverter
    fun listToJsonString(value: List<YourModel>?): String = Gson().toJson(value)

    @TypeConverter
    fun jsonStringToList(value: String) = Gson().fromJson(value, Array<YourModel>::class.java).toList()
}

Step 2 :

@Database(entities = [YourEntity::class], version = 1)
@TypeConverters(Converters::class)
abstract class YourDatabase : RoomDatabase() {
     abstract fun yourDao(): YourDao
}

Step 3 :

Note: You do not need to call functions of Converter which are listToJsonString() and jsonStringToList(). They are using in background by Room.

@Entity(tableName = "example_database_table") 
data class YourEntity(
  @PrimaryKey(autoGenerate = true) val id: Long = 0,
  @ColumnInfo(name = "your_model_list") var yourModelList: List<YourModel>,
)

Upvotes: 21

Tarun Anchala
Tarun Anchala

Reputation: 2702

All above answers are for list of strings. But below helps you to write converter for list of objects.

Just in place of "YourClassName", add your Object class.

 @TypeConverter
        public String fromValuesToList(ArrayList<**YourClassName**> value) {
            if (value== null) {
                return (null);
            }
            Gson gson = new Gson();
            Type type = new TypeToken<ArrayList<**YourClassName**>>() {}.getType();
            return gson.toJson(value, type);
        }
    
        @TypeConverter
        public ArrayList<**YourClassName**> toOptionValuesList(String value) {
            if (value== null) {
                return (null);
            }
            Gson gson = new Gson();
            Type type = new TypeToken<List<**YourClassName**>>() {
            }.getType();
            return gson.fromJson(value, type);
        }

Upvotes: 1

Patrick
Patrick

Reputation: 1045

Native Kotlin version using Kotlin's serialization component – kotlinx.serialization.

  1. Add the Kotlin serialization Gradle plugin and dependency to your build.gradle:
apply plugin: 'kotlinx-serialization'

dependencies {
   ...
   implementation "org.jetbrains.kotlinx:kotlinx-serialization-json:1.0.1"
}
  1. Add the Type converters to your Converter class;
class Converters {
   @TypeConverter
   fun fromList(value : List<String>) = Json.encodeToString(value)

   @TypeConverter
   fun toList(value: String) = Json.decodeFromString<List<String>>(value)
}
  1. Add your Converter class to your database class:
@TypeConverters(Converters::class)
abstract class YourDatabase: RoomDatabase() {...}

And you're done!

Extra resources:

Upvotes: 45

Albert Gom&#224;
Albert Gom&#224;

Reputation: 331

I would personally advise against @TypeConverters/serializations, since they break the database's normal forms compliance.

For this particular case it might be worth defining a relationship using the @Relation annotation, which allows to query nested entities into a single object without the added complexity of declaring a @ForeignKey and writing all the SQL queries manually:

@Entity
public class MainActivityData {
    @PrimaryKey
    private String userId;
    private String itemOneId;
    private String itemTwoId;
}

@Entity
public class MyListItem {
    @PrimaryKey
    public int id;
    public String ownerUserId;
    public String text;
}

/* This is the class we use to define our relationship,
   which will also be used to return our query results.
   Note that it is not defined as an @Entity */
public class DataWithItems {
    @Embedded public MainActivityData data;
    @Relation(
        parentColumn = "userId"
        entityColumn = "ownerUserId"
    )
    public List<MyListItem> myListItems;
}

/* This is the DAO interface where we define the queries.
   Even though it looks like a single SELECT, Room performs
   two, therefore the @Transaction annotation is required */
@Dao
public interface ListItemsDao {
    @Transaction
    @Query("SELECT * FROM MainActivityData")
    public List<DataWithItems> getAllData();
}

Aside from this 1-N example, it is possible to define 1-1 and N-M relationships as well.

Upvotes: 19

Amit Bhandari
Amit Bhandari

Reputation: 3134

Type Converter are made specifically for that. In your case, you can use code snippet given below to store data in DB.

public class Converters {
    @TypeConverter
    public static ArrayList<String> fromString(String value) {
        Type listType = new TypeToken<ArrayList<String>>() {}.getType();
        return new Gson().fromJson(value, listType);
    }

    @TypeConverter
    public static String fromArrayList(ArrayList<String> list) {
        Gson gson = new Gson();
        String json = gson.toJson(list);
        return json;
    }
}

And mention this class in your Room DB like this

@Database (entities = {MainActivityData.class},version = 1)
@TypeConverters({Converters.class})

More info here

Upvotes: 173

w201
w201

Reputation: 2228

All answers above correct. Yes, if you REALLY need store array of something into one SQLite field TypeConverter is a solution.

And I used the accepted answer in my projects.

But don't do it!!!

If you need store array in Entity in 90% cases you need to create one-to-many or many-to-many relationships.

Otherwise, your next SQL query for select something with key inside this array will be absolutely hell...

Example:

Object foo comes as json: [{id: 1, name: "abs"}, {id:2, name: "cde"}

Object bar: [{id, 1, foos: [1, 2], {...}]

So don't make entity like:

@Entity....
data class bar(
...
val foos: ArrayList<Int>)

Make like next:

@Entity(tablename="bar_foo", primaryKeys=["fooId", "barId"])
data class barFoo(val barId: Int, val fooId: Int)

And sore your foos:[] as records in this table.

Upvotes: 0

Awscoolboy
Awscoolboy

Reputation: 36

 @Query("SELECT * FROM business_table")
 abstract List<DatabaseModels.Business> getBusinessInternal();


 @Transaction @Query("SELECT * FROM business_table")
 public ArrayList<DatabaseModels.Business> getBusiness(){
        return new ArrayList<>(getBusinessInternal());
 }

Upvotes: 0

Manohar
Manohar

Reputation: 23384

Kotlin version for type converter:

 class Converters {

    @TypeConverter
    fun listToJson(value: List<JobWorkHistory>?) = Gson().toJson(value)

    @TypeConverter
    fun jsonToList(value: String) = Gson().fromJson(value, Array<JobWorkHistory>::class.java).toList()
}

I Used JobWorkHistory object for my purpose, use the object of your own

@Database(entities = arrayOf(JobDetailFile::class, JobResponse::class), version = 1)
@TypeConverters(Converters::class)
abstract class MyRoomDataBase : RoomDatabase() {
     abstract fun attachmentsDao(): AttachmentsDao
}

Upvotes: 78

Hamid Zandi
Hamid Zandi

Reputation: 2902

in my case problem was generic type base on this answer

https://stackoverflow.com/a/48480257/3675925 use List instead of ArrayList

 import androidx.room.TypeConverter
 import com.google.gson.Gson 
 import com.google.gson.reflect.TypeToken
 class IntArrayListConverter {
     @TypeConverter
     fun fromString(value: String): List<Int> {
         val type = object: TypeToken<List<Int>>() {}.type
         return Gson().fromJson(value, type)
     }

     @TypeConverter
     fun fromArrayList(list: List<Int>): String {
         val type = object: TypeToken<List<Int>>() {}.type
         return Gson().toJson(list, type)
     } 
}

it doesn't need add @TypeConverters(IntArrayListConverter::class) to query in dao class nor fields in Entity class and just add @TypeConverters(IntArrayListConverter::class) to database class

@Database(entities = [MyEntity::class], version = 1, exportSchema = false)
@TypeConverters(IntArrayListConverter::class)
abstract class MyDatabase : RoomDatabase() {

Upvotes: 3

user7680587
user7680587

Reputation: 95

Here is the example for adding the customObject types to Room DB table. https://mobikul.com/insert-custom-list-and-get-that-list-in-room-database-using-typeconverter/

Adding a type converter was easy, I just needed a method that could turn the list of objects into a string, and a method that could do the reverse. I used gson for this.

public class Converters {

    @TypeConverter
    public static String MyListItemListToString(List<MyListitem> list) {
        Gson gson = new Gson();
        return gson.toJson(list);
    }

    @TypeConverter
    public static List<Integer> stringToMyListItemList(@Nullable String data) {
        if (data == null) {
            return Collections.emptyList();
        }

        Type listType = new TypeToken<List<MyListItem>>() {}.getType();

        Gson gson = new Gson();
        return gson.fromJson(data, listType);
    }
}

I then added an annotation to the field in the Entity:

@TypeConverters(Converters.class)

public final ArrayList<MyListItem> myListItems;

Upvotes: 1

Derrick Njeru
Derrick Njeru

Reputation: 161

This is how i handle List conversion

public class GenreConverter {
@TypeConverter
public List<Integer> gettingListFromString(String genreIds) {
    List<Integer> list = new ArrayList<>();

    String[] array = genreIds.split(",");

    for (String s : array) {
       if (!s.isEmpty()) {
           list.add(Integer.parseInt(s));
       }
    }
    return list;
}

@TypeConverter
public String writingStringFromList(List<Integer> list) {
    String genreIds = "";
    for (int i : list) {
        genreIds += "," + i;
    }
    return genreIds;
}}

And then on the database i do as shown below

@Database(entities = {MovieEntry.class}, version = 1)
@TypeConverters(GenreConverter.class)

And below is a kotlin implementation of the same;

class GenreConverter {
@TypeConverter
fun gettingListFromString(genreIds: String): List<Int> {
    val list = mutableListOf<Int>()

    val array = genreIds.split(",".toRegex()).dropLastWhile {
        it.isEmpty()
    }.toTypedArray()

    for (s in array) {
        if (s.isNotEmpty()) {
            list.add(s.toInt())
        }
    }
    return list
}

@TypeConverter
fun writingStringFromList(list: List<Int>): String {
    var genreIds=""
    for (i in list) genreIds += ",$i"
    return genreIds
}}

Upvotes: 11

Nitin Misra
Nitin Misra

Reputation: 4522

Better version of List<String> converter 

class StringListConverter {
    @TypeConverter
    fun fromString(stringListString: String): List<String> {
        return stringListString.split(",").map { it }
    }

    @TypeConverter
    fun toString(stringList: List<String>): String {
        return stringList.joinToString(separator = ",")
    }
}

Upvotes: 28

Dokuzov
Dokuzov

Reputation: 158

Json conversions don't scale well in terms of memory allocation.I'd rather go for something similar to responses above with some nullability.

class Converters {
    @TypeConverter
    fun stringAsStringList(strings: String?): List<String> {
        val list = mutableListOf<String>()
        strings
            ?.split(",")
            ?.forEach {
                list.add(it)
            }

        return list
    }

    @TypeConverter
    fun stringListAsString(strings: List<String>?): String {
        var result = ""
        strings?.forEach { element ->
            result += "$element,"
        }
        return result.removeSuffix(",")
    }
}

For simple data types the above can be used, otherwise for complex datatypes Room provides Embedded

Upvotes: 0

Daniel Wilson
Daniel Wilson

Reputation: 19824

This answer uses Kotin to split by comma and construct the comma delineated string. The comma needs to go at the end of all but the last element, so this will handle single element lists as well. 

object StringListConverter {
        @TypeConverter
        @JvmStatic
        fun toList(strings: String): List<String> {
            val list = mutableListOf<String>()
            val array = strings.split(",")
            for (s in array) {
                list.add(s)
            }
            return list
        }

        @TypeConverter
        @JvmStatic
        fun toString(strings: List<String>): String {
            var result = ""
            strings.forEachIndexed { index, element ->
                result += element
                if(index != (strings.size-1)){
                    result += ","
                }
            }
            return result
        }
    }

Upvotes: 4

abitcode
abitcode

Reputation: 1582

Adding @TypeConverters with the converter class as params

to Database & to the Dao class, made my queries work

Upvotes: 0

live-love
live-love

Reputation: 52366

Had the same error message as described above. I would like to add: if you get this error message in a @Query, you should add @TypeConverters above the @Query annotation.

Example:

@TypeConverters(DateConverter.class)
@Query("update myTable set myDate=:myDate  where id = :myId")
void updateStats(int myId, Date myDate);

....

public class DateConverter {

    @TypeConverter
    public static Date toDate(Long timestamp) {
        return timestamp == null ? null : new Date(timestamp);
    }

    @TypeConverter
    public static Long toTimestamp(Date date) {
        return date == null ? null : date.getTime();
    }
}

Upvotes: 6

CommonsWare
CommonsWare

Reputation: 1006584

Option #1: Have MyListItems be an @Entity, as MainActivityData is. MyListItems would set up a @ForeignKey back to MainActivityData. In this case, though, MainActivityData cannot have private ArrayList<MyListItems> myListItems, as in Room, entities do not refer to other entities. A view model or similar POJO construct could have a MainActivityData and its associated ArrayList<MyListItems>, though.

Option #2: Set up a pair of @TypeConverter methods to convert ArrayList<MyListItems> to and from some basic type (e.g., a String, such as by using JSON as a storage format). Now, MainActivityData can have its ArrayList<MyListItems> directly. However, there will be no separate table for MyListItems, and so you cannot query on MyListItems very well.

Upvotes: 104

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