java - Android：如何从 sqlite 数据库中检索数据

Question

我一直在研究用于 sqlite 数据库的 android sdk 的信息和文档，但我仍然有点卡住。我有一个从此处找到的示例中检索到的数据库类。这是我的课：

package com.example.medtracker;

import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.Calendar;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBAdapter {
    private static final String DATABASE_NAME = "meds.db";
    private String DATABASE_TABLE;
    private static final int DATABASE_VERSION = 1;

    // Index Key column
    public static final String KEY_ID = "_id";

    // Name of the column index of each column in DB
    public ArrayList<String> TABLE_KEYS = new ArrayList<String>();
    public ArrayList<String> TABLE_OPTIONS = new ArrayList<String>();
    public final String KEY_TIMESTAMP = "timeStamp";
    public final int TIMESTAMP_COLUMN = 1;

    // Create new database
    private String DATABASE_CREATE;

    // Variable to hold database instant
    private SQLiteDatabase db;

    // Database open/upgrade helper
    private myDBHelper dbHelper;

    public DBAdapter(Context context, String table, ArrayList<String> keys,
            ArrayList<String> options) {
        // Start initializing all of the variables
        DATABASE_TABLE = table;
        TABLE_KEYS = (ArrayList<String>) keys.clone();
        TABLE_OPTIONS = options;

        String keyString = "";
        for (int i = 0; TABLE_KEYS.size() > i; i++) {

            // Add commas to the options elements if there is a next value.
            if (i + 1 < TABLE_OPTIONS.size() && TABLE_OPTIONS.get(i) != null) {
                TABLE_OPTIONS.set(i, TABLE_OPTIONS.get(i) + ",");
            } else if (i + 1 == TABLE_OPTIONS.size()
                    && TABLE_OPTIONS.get(i) != null) {
                if (i + 1 < TABLE_KEYS.size()) {
                    TABLE_OPTIONS.set(i, TABLE_OPTIONS.get(i) + ",");
                } else {
                    TABLE_KEYS.set(i, TABLE_KEYS.get(i) + "");
                }
            } else if (i + 1 != TABLE_KEYS.size()) {
                TABLE_KEYS.set(i, TABLE_KEYS.get(i) + ",");
            } else {
                TABLE_KEYS.set(i, TABLE_KEYS.get(i) + "");
            }

            System.out.println(TABLE_OPTIONS.toString());
            System.out.println(TABLE_KEYS.toString());

            if (i + 1 <= TABLE_OPTIONS.size() && TABLE_OPTIONS.get(i) != null)
                keyString = keyString + " " + TABLE_KEYS.get(i) + " "
                        + TABLE_OPTIONS.get(i);
            else if (i + 1 > TABLE_OPTIONS.size()
                    || TABLE_OPTIONS.get(i) == null) {
                keyString = keyString + " " + TABLE_KEYS.get(i);
            }
        }

        // Create the database creation string.
        DATABASE_CREATE = "CREATE TABLE IF NOT EXISTS " + DATABASE_TABLE + " ("
                + "_id" + " INTEGER PRIMARY KEY AUTOINCREMENT, "
                + KEY_TIMESTAMP + "," + keyString + ");";

        // Create a new Helper
        dbHelper = new myDBHelper(context, DATABASE_NAME, null,
                DATABASE_VERSION, DATABASE_TABLE, DATABASE_CREATE);
    }

    public DBAdapter open() throws SQLException {
        db = dbHelper.getWritableDatabase();
        return this;
    }

    public void close() {
        db.close();
    }

    public long insertEntry(ArrayList<String> key, ArrayList<String> value) {
        String timeStamp = new Timestamp(Calendar.getInstance()
                .getTimeInMillis()).toString();
        ContentValues contentValues = new ContentValues();
        for (int i = 0; key.size() > i; i++) {
            contentValues.put(key.get(i), value.get(i));
        }
        contentValues.put(KEY_TIMESTAMP, timeStamp);
        return db.insert(DATABASE_TABLE, null, contentValues);
    }

    public boolean removeEntry(long rowIndex) {
        return db.delete(DATABASE_TABLE, KEY_ID + "=" + rowIndex, null) > 0;
    }

    public Cursor getAllEntries(String[] columns, String selection,
            String[] selectionArgs, String groupBy, String having,
            String sortBy, String sortOption) {
        return db.query(DATABASE_TABLE, columns, selection, selectionArgs,
                groupBy, having, sortBy + " " + sortOption);
    }

    public int updateEntry(long rowIndex, ArrayList<String> key,
            ArrayList<String> value) {
        String timeStamp = new Timestamp(Calendar.getInstance()
                .getTimeInMillis()).toString();
        String where = KEY_ID + "=" + rowIndex;
        ContentValues contentValues = new ContentValues();
        for (int i = 0; key.size() > i; i++) {
            contentValues.put(key.get(i), value.get(i));
        }
        contentValues.put(KEY_TIMESTAMP, timeStamp);
        return db.update(DATABASE_TABLE, contentValues, where, null);
    }

    public boolean clearTable() {
        return db.delete(DATABASE_TABLE, null, null) > 0;
    }

    private static class myDBHelper extends SQLiteOpenHelper {
        private String creationString;
        private String tableName;
        @SuppressWarnings("unused")
        SQLiteDatabase db;

        /**
         * Creates a myDBHelper object.
         * 
         * @param context
         *            The context where the access is needed
         * @param name
         *            Name of database file
         * @param factory
         *            A CursorFactory, or null to use default CursorFactory
         * @param version
         *            Database version
         * @param tableName
         *            Name of table within database
         * @param creationString
         *            SQL String used to create the database
         */
        public myDBHelper(Context context, String name, CursorFactory factory,
                int version, String tableName, String creationString) {
            super(context, name, factory, version);
            this.creationString = creationString;
            this.tableName = tableName;
        }

        /**
         * Creates the database table.
         * 
         * @param db
         *            The database used by this helper to create the table in
         */
        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(creationString);
        }

        /**
         * This method determines if the database needs to be updated or not.
         * 
         * @param db
         *            The database used by this helper
         * @param oldVersion
         *            The old database version
         * @param newVersion
         *            The new database version
         */
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            // Log the version upgrade
            Log.w("TaskDBAdapter", "Upgrading from version " + oldVersion
                    + " to " + newVersion + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS " + tableName);
            onCreate(db);

        }

        /**
         * Creates tables when the database is opened if the tables need to be
         * created.
         * 
         * @param db
         *            The database used by this helper
         */
        @Override
        public void onOpen(SQLiteDatabase db) {
            db.execSQL(creationString);
        }

    }
}

然后我做了一个类来添加对象： public class AddMed extends Activity implements OnClickListener {

Button submit;
    EditText name, dossage;
    DBAdapter database;
    String names, amount;
    String total;
    ArrayList<String> btr;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.addmed);
        submit = (Button) findViewById(R.id.bSubmit);
        name = (EditText) findViewById(R.id.etNameOfMed);
        dossage = (EditText) findViewById(R.id.etHowMuch);
    }

    @Override
    public void onClick(View arg0) {
        // TODO Auto-generated method stub
        switch (arg0.getId()) {
        case R.id.bSubmit:
            names = name.getText().toString();
            amount = dossage.getText().toString();
            total = names + amount;
            btr.add(total);
            database.open();
            database.insertEntry(btr, btr);
            database.close();
            break;
        }
    }

}

然后我有另一个带有文本视图的类，我尝试创建一个新的 DBAdatper 实例并使用光标中的 getAllEntries 方法，但我对参数感到困惑。有人可以启发我吗？感谢您的帮助。

Answer 1

您引用的示例似乎只是试图充当SQLLiteDatabase类的包装器。该示例列出了 getAllEntries 中每个参数的用途。似乎有很多参数，但如果您不想对结果集进行分组或排序，其中一些参数可以为空。以下是每个参数的作用列表，取自SQLLiteDatabase API：

Answer 2

你找到的教程提供了一个试图自动为你做很多事情的类：如果你得到它很好，但如果你没有得到它就不是很好。

我建议你放弃这个非常复杂的例子，而是自己从头开始，使用更合适的教程。 http://www.vogella.com/有很多很好的教程，包括 SQLite 数据库：SQLite

Answer 3

从SQLiteDatabase 文档中查询

public Cursor query (String table, String[] columns, String selection, String[]
selectionArgs, String groupBy, String having, String orderBy, String limit)

Added in API level 1

Query the given table, returning a Cursor over the result set.

Parameters

table       The table name to compile the query against.

columns     A list of which columns to return. Passing null will return all
            columns, which is discouraged to prevent reading data from storage
            that isn't going to be used.

selection   A filter declaring which rows to return, formatted as an SQL WHERE
            clause (excluding the WHERE itself). Passing null will return all rows for
            the given table.

selectionArgs   You may include ?s in selection, which will be replaced by the
                values from selectionArgs, in order that they appear in the
                selection. The values will be bound as Strings.

groupBy     A filter declaring how to group rows, formatted as an SQL GROUP BY 
            clause (excluding the GROUP BY itself). Passing null will cause the rows
            to not be grouped.

having      A filter declare which row groups to include in the cursor, if row
            grouping is being used, formatted as an SQL HAVING clause (excluding the
            HAVING itself). Passing null will cause all row groups to be included,
            and is required when row grouping is not being used.

orderBy     How to order the rows, formatted as an SQL ORDER BY clause (excluding
            the ORDER BY itself). Passing null will use the default sort order, which
            may be unordered.

limit       Limits the number of rows returned by the query, formatted as LIMIT
            clause. Passing null denotes no LIMIT clause.

假设您有一个名为 table1 的表，其中包含名为 x、y、z 的三列。你想做以下声明：

SELECT x,y FROM table1 WHERE x = 'squirrels' AND y = 'cats';

表参数只是表的名称（“table1”）。columns 参数将是您有兴趣获取其值的列（在本例中为“x”和“y”列）。选择参数将是“x = ? AND y = ?”。selectionArgs 参数将是一个包含“squirrels”和“cats”的数组。如果你知道 SQL，其余的就很容易解释了。