java - 尝试预填充房间数据库
问题描述
我正在尝试构建一个具有两个具有一对多关系的表的数据库。(一个食谱属于多种成分)
看起来我已经正确设置了我认为的所有内容,但是现在当我构建数据库时,我想要预填充一些食谱和属于该食谱的成分。但我不知道如何在数据库构建器中实现这一点。
这是我的食谱表:
@Entity(tableName = "recipe_table") //Represents the table in SQLite database
public class Recipe {
@PrimaryKey(autoGenerate = true)
private int id; //Holds the id of the recipe
private String title; //Holds the name of the recipe
@Ignore
private List<Ingredient> ingredientsList;
//Generate constructor to create objects later
public Recipe(String title, List<Ingredient> ingredientsList) {
this.title = title;
this.ingredientsList = ingredientsList;
}
//Generate getters to persist values to the database
public int getId() {
return id;
}
//Generate setter so that room can recreate later
public void setId(int id) {
this.id = id;
}
public String getTitle() {
return title;
}
public List<Ingredient> getIngredientsList() {
return ingredientsList;
}
public void setIngredientsList(List<Ingredient> ingredientsList) {
this.ingredientsList = ingredientsList;
}
}
成分表:
package com.example.kookrecepten;
import androidx.room.Entity;
import androidx.room.ForeignKey;
import androidx.room.Ignore;
import androidx.room.PrimaryKey;
import java.util.List;
import static androidx.room.ForeignKey.CASCADE;
@Entity(foreignKeys = @ForeignKey(entity = Recipe.class, parentColumns = "id", childColumns = "recipeId", onDelete = CASCADE))
public class Ingredient {
@PrimaryKey
private int id;
private int recipeId;
private String title; //Name of the ingredient
@Ignore
private List<Ingredient> ingredientsList;
public Ingredient(String title, int recipeId) {
this.title = title;
this.recipeId = recipeId;
}
public void setId(int id) {
this.id = id;
}
public void setRecipeId(int recipeId) {
this.recipeId = recipeId;
}
public int getId() {
return id;
}
public int getRecipeId() {
return recipeId;
}
public String getTitle() {
return title;
}
}
这是我的 dao 文件
@Dao
public abstract class RecipeDao {
//Insert recipe
@Insert
public abstract void insertRecipe(Recipe recipe);
//Insert ingredients list
@Insert
public abstract void insertIngredientList(List<Ingredient> ingredients);
@Query("SELECT * FROM recipe_table WHERE id =:id")
public abstract Recipe getRecipe(int id);
@Query("SELECT * FROM Ingredient WHERE recipeId =:recipeId")
public abstract List<Ingredient> getIngredientList(int recipeId);
public void insertRecipeWithIngredients(Recipe recipe) {
List<Ingredient> ingredients = recipe.getIngredientsList();
for (int i = 0; i < ingredients.size(); i++) {
ingredients.get(i).setRecipeId(recipe.getId());
}
insertIngredientList(ingredients);
insertRecipe(recipe);
}
public Recipe getRecipeWithIngredients(int id) {
Recipe recipe = getRecipe(id);
List<Ingredient> ingredients = getIngredientList(id);
recipe.setIngredientsList(ingredients);
return recipe;
}
}
但我的问题是我不知道如何预填充我的数据库。
private static class PopulateDbAsyncTask extends AsyncTask<Void, Void, Void> {
private RecipeDao recipeDao;
private PopulateDbAsyncTask(RecipeDatabase db) {
recipeDao = db.recipeDao();
}
@Override
protected Void doInBackground(Void... voids) {
recipeDao.insertRecipeWithIngredients(
//insert a recipe and a list of ingredients?
);
return null;
}
}
解决方案
首先,我建议您不要 AsyncTask 因为它已弃用。点击官方文档了解更多详情。
其次,您有 3 个用于预填充数据库的选项,如下所示:
1) createFromAssets:在此选项中,您可以在 assets 文件夹下创建一个名为“databases”的目录,因此您可以如下所示:
.createFromAssets("/databases/YOUR DATABASE FILENAME")
2) createFromFile:此选项可能适用于您分配其路径的文件。
.createFromFile(File("YOUR FILE PATH"))
如果您对这两种解决方案感到困惑,您可以尝试手动解决方案,我们可以称之为手动解决方案是的!通过访问资产文件夹中的数据库文件。
private fun copyDBFromStorage(databaseName: String) {
if (checkIfDBExists(this, databaseName)) return
val databaseFile = File(this.getDatabasePath(databaseName).toString())
val sourceLocation = assets.open("Your database file path")
try {
val inputStream = sourceLocation
val os = FileOutputStream(databaseFile)
val buffer = ByteArray(1024 * 32)
var length = inputStream.read(buffer)
while (length > 0) {
os.write(buffer, 0, length)
length = inputStream.read(buffer)
}
os.flush()
os.close()
inputStream.close()
} catch (ex: IOException) {
ex.printStackTrace();
throw RuntimeException("Error copying storage database");
}
}
private fun checkIfDBExists(
context: Context,
databaseName: String
): Boolean {
val dbfile = File(context.getDatabasePath(databaseName).toString())
if (dbfile.exists()) return true
if (!dbfile.parentFile.exists()) {
dbfile.parentFile.mkdirs()
}
return false
}
我希望这会有所帮助
快乐编码
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