java 阳光数据库创建

Posted 2021-05-08

package com.example.android.sunshine.data;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

import com.example.android.sunshine.data.WeatherContract.WeatherEntry;

/**
 * Manages a local database for weather data.
 */

// COMPLETED (11) Extend SQLiteOpenHelper from WeatherDbHelper
public class WeatherDbHelper extends SQLiteOpenHelper {

//  COMPLETED (12) Create a public static final String called DATABASE_NAME with value "weather.db"
    /*
     * This is the name of our database. Database names should be descriptive and end with the
     * .db extension.
     */
    public static final String DATABASE_NAME = "weather.db";

//  COMPLETED (13) Create a private static final int called DATABASE_VERSION and set it to 1
    /*
     * If you change the database schema, you must increment the database version or the onUpgrade
     * method will not be called.
     *
     * The reason DATABASE_VERSION starts at 3 is because Sunshine has been used in conjunction
     * with the Android course for a while now. Believe it or not, older versions of Sunshine
     * still exist out in the wild. If we started this DATABASE_VERSION off at 1, upgrading older
     * versions of Sunshine could cause everything to break. Although that is certainly a rare
     * use-case, we wanted to watch out for it and warn you what could happen if you mistakenly
     * version your databases.
     */
    private static final int DATABASE_VERSION = 1;

//  COMPLETED (14) Create a constructor that accepts a context and call through to the superclass constructor
    public WeatherDbHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

//  COMPLETED (15) Override onCreate and create the weather table from within it
    /**
     * Called when the database is created for the first time. This is where the creation of
     * tables and the initial population of the tables should happen.
     *
     * @param sqLiteDatabase The database.
     */
    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {

        /*
         * This String will contain a simple SQL statement that will create a table that will
         * cache our weather data.
         */
        final String SQL_CREATE_WEATHER_TABLE =

                "CREATE TABLE " + WeatherEntry.TABLE_NAME + " (" +

                /*
                 * WeatherEntry did not explicitly declare a column called "_ID". However,
                 * WeatherEntry implements the interface, "BaseColumns", which does have a field
                 * named "_ID". We use that here to designate our table's primary key.
                 */
                WeatherEntry._ID               + " INTEGER PRIMARY KEY AUTOINCREMENT, " +

                WeatherEntry.COLUMN_DATE       + " INTEGER, "                 +

                WeatherEntry.COLUMN_WEATHER_ID + " INTEGER, "                 +

                WeatherEntry.COLUMN_MIN_TEMP   + " REAL, "                    +
                WeatherEntry.COLUMN_MAX_TEMP   + " REAL, "                    +

                WeatherEntry.COLUMN_HUMIDITY   + " REAL, "                    +
                WeatherEntry.COLUMN_PRESSURE   + " REAL, "                    +

                WeatherEntry.COLUMN_WIND_SPEED + " REAL, "                    +
                WeatherEntry.COLUMN_DEGREES    + " REAL" + ");";

        /*
         * After we've spelled out our SQLite table creation statement above, we actually execute
         * that SQL with the execSQL method of our SQLite database object.
         */
        sqLiteDatabase.execSQL(SQL_CREATE_WEATHER_TABLE);
    }

//  COMPLETED (16) Override onUpgrade, but don't do anything within it yet
    /**
     * This database is only a cache for online data, so its upgrade policy is simply to discard
     * the data and call through to onCreate to recreate the table. Note that this only fires if
     * you change the version number for your database (in our case, DATABASE_VERSION). It does NOT
     * depend on the version number for your application found in your app/build.gradle file. If
     * you want to update the schema without wiping data, commenting out the current body of this
     * method should be your top priority before modifying this method.
     *
     * @param sqLiteDatabase Database that is being upgraded
     * @param oldVersion     The old database version
     * @param newVersion     The new database version
     */
    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {

    }
}

package com.example.android.sunshine.data;

import android.provider.BaseColumns;

/**
 * Defines table and column names for the weather database. This class is not necessary, but keeps
 * the code organized.
 */
public class WeatherContract {

//  COMPLETED (1) Within WeatherContract, create a public static final class called WeatherEntry that implements BaseColumns
    /* Inner class that defines the table contents of the weather table */
    public static final class WeatherEntry implements BaseColumns {

//      Do steps 2 through 10 within the WeatherEntry class

//      COMPLETED (2) Create a public static final String call TABLE_NAME with the value "weather"

        /* Used internally as the name of our weather table. */
        public static final String TABLE_NAME = "weather";

//      COMPLETED (3) Create a public static final String call COLUMN_DATE with the value "date"
        /*
         * The date column will store the UTC date that correlates to the local date for which
         * each particular weather row represents. For example, if you live in the Eastern
         * Standard Time (EST) time zone and you load weather data at 9:00 PM on September 23, 2016,
         * the UTC time stamp for that particular time would be 1474678800000 in milliseconds.
         * However, due to time zone offsets, it would already be September 24th, 2016 in the GMT
         * time zone when it is 9:00 PM on the 23rd in the EST time zone. In this example, the date
         * column would hold the date representing September 23rd at midnight in GMT time.
         * (1474588800000)
         *
         * The reason we store GMT time and not local time is because it is best practice to have a
         * "normalized", or standard when storing the date and adjust as necessary when
         * displaying the date. Normalizing the date also allows us an easy way to convert to
         * local time at midnight, as all we have to do is add a particular time zone's GMT
         * offset to this date to get local time at midnight on the appropriate date.
         */
        public static final String COLUMN_DATE = "date";

//      COMPLETED (4) Create a public static final String call COLUMN_WEATHER_ID with the value "weather_id"
        /* Weather ID as returned by API, used to identify the icon to be used */
        public static final String COLUMN_WEATHER_ID = "weather_id";

//      COMPLETED (5) Create a public static final String call COLUMN_MIN_TEMP with the value "min"
        /* Min and max temperatures in °C for the day (stored as floats in the database) */
        public static final String COLUMN_MIN_TEMP = "min";
//      COMPLETED (6) Create a public static final String call COLUMN_MAX_TEMP with the value "max"
        public static final String COLUMN_MAX_TEMP = "max";

//      COMPLETED (7) Create a public static final String call COLUMN_HUMIDITY with the value "humidity"
        /* Humidity is stored as a float representing percentage */
        public static final String COLUMN_HUMIDITY = "humidity";

//      COMPLETED (8) Create a public static final String call COLUMN_PRESSURE with the value "pressure"
        /* Pressure is stored as a float representing percentage */
        public static final String COLUMN_PRESSURE = "pressure";

//      COMPLETED (9) Create a public static final String call COLUMN_WIND_SPEED with the value "wind"
        /* Wind speed is stored as a float representing wind speed in mph */
        public static final String COLUMN_WIND_SPEED = "wind";

//      COMPLETED (10) Create a public static final String call COLUMN_DEGREES with the value "degrees"
        /*
         * Degrees are meteorological degrees (e.g, 0 is north, 180 is south).
         * Stored as floats in the database.
         *
         * Note: These degrees are not to be confused with temperature degrees of the weather.
         */
        public static final String COLUMN_DEGREES = "degrees";
    }
}