使用一个ContentProvider操作多张表
在我们开发过程中，通常使用ContentProvider来操作数据。查询数据库中的一张表的数据我们创建一个ContentProvider提供操作，需要访问多张表中的数据时，可以创建多个对应的ContentProvider来操作数据。
当然，如果只用一个ContentProvider来操作同一个数据库中的多张表也是可以实现的。ContentProvider所提供的CRUD方法都是通过uri来实现，使用一个ContentProvider操作多张表，也就是说一个authority，然后多个CONTENT_URI对应多张表。思路大概就是这样子，下面给出代码，代码是在NotePad源码上做了修改：
NotePad类（契约类）中声明AUTHORITY,class Notes对应数据库中的Notes表，class NotesGroup对应 NotesGroup表，它们有各自的CONTENT_URI。
NotePad.java
public final class NotePad {
public static final String AUTHORITY = "com.google.provider.NotePad";
// This class cannot be instantiated
private NotePad() {
}
/** * Notes table contract */
public static final class Notes implements BaseColumns {
// This class cannot be instantiated
private Notes() {}
/** * The table name offered by this provider */
public static final String TABLE_NAME = "notes";
/* * URI definitions */
/** * The scheme part for this provider's URI */
private static final String SCHEME = "content://";
/** * Path parts for the URIs */
/** * Path part for the Notes URI */
private static final String PATH_NOTES = "/notes";
/** * Path part for the Note ID URI */
private static final String PATH_NOTE_ID = "/notes/";
/** * 0-relative position of a note ID segment in the path part of a note ID URI */
public static final int NOTE_ID_PATH_POSITION = 1;
/** * Path part for the Live Folder URI */
private static final String PATH_LIVE_FOLDER = "/live_folders/notes";
/** * The content:// style URL for this table */
public static final Uri CONTENT_URI = Uri.parse(SCHEME + AUTHORITY + PATH_NOTES);
/** * The content URI base for a single note. Callers must * append a numeric note id to this Uri to retrieve a note */
public static final Uri CONTENT_ID_URI_BASE
= Uri.parse(SCHEME + AUTHORITY + PATH_NOTE_ID);
/** * The content URI match pattern for a single note, specified by its ID. Use this to match * incoming URIs or to construct an Intent. */
public static final Uri CONTENT_ID_URI_PATTERN
= Uri.parse(SCHEME + AUTHORITY + PATH_NOTE_ID + "/#");
/** * The content Uri pattern for a notes listing for live folders */
public static final Uri LIVE_FOLDER_URI
= Uri.parse(SCHEME + AUTHORITY + PATH_LIVE_FOLDER);
/* * MIME type definitions */
/** * The MIME type of {@link #CONTENT_URI} providing a directory of notes. */
public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.google.note";
/** * The MIME type of a {@link #CONTENT_URI} sub-directory of a single * note. */
public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item/vnd.google.note";
/** * The default sort order for this table */
public static final String DEFAULT_SORT_ORDER = "modified DESC";
/* * Column definitions */
/** * Column name for the title of the note * <P>Type: TEXT</P> */
public static final String COLUMN_NAME_TITLE = "title";
/** * Column name of the note content * <P>Type: TEXT</P> */
public static final String COLUMN_NAME_NOTE = "note";
/** * Column name for the creation timestamp * <P>Type: INTEGER (long from System.curentTimeMillis())</P> */
public static final String COLUMN_NAME_CREATE_DATE = "created";
/** * Column name for the modification timestamp * <P>Type: INTEGER (long from System.curentTimeMillis())</P> */
public static final String COLUMN_NAME_MODIFICATION_DATE = "modified";
public static final String COLUMN_NAME_GROUPID = "gid";
}
public static final class NotesGroup implements BaseColumns {
private NotesGroup(){}
public static final String TABLE_NAME = "notesGroup";
private static final String SCHEME = "content://";
private static final String PATH_NOTES_GROUP = "/notesGroup";
private static final String PATH_NOTEGROUP_ID = "/notesGroup/";
/** * 0-relative position of a note ID segment in the path part of a note ID URI */
public static final int NOTE_ID_PATH_POSITION = 1;
/** * The content:// style URL for this table */
public static final Uri CONTENT_URI = Uri.parse(SCHEME + AUTHORITY + PATH_NOTES_GROUP);
public static final Uri CONTENT_ID_URI_BASE
= Uri.parse(SCHEME + AUTHORITY + PATH_NOTEGROUP_ID);
public static final Uri CONTENT_ID_URI_PATTERN
= Uri.parse(SCHEME + AUTHORITY + PATH_NOTEGROUP_ID + "/#");
public static final String COLUMN_NAME_GROUPTITLE = "name";
}1、在自定义ContentProvider类给sUriMatcher添加匹配项(两张表的匹配)
//Notes表
private static final int NOTES = 1;
private static final int NOTE_ID = 2;
//NotesGroup表
private static final int NotesGroup = 4;
private static final int NotesGroup_ID = 5;
sUriMatcher.addURI(NotePad.AUTHORITY, "notes", NOTES);
sUriMatcher.addURI(NotePad.AUTHORITY, "notes/#", NOTE_ID);
sUriMatcher.addURI(NotePad.AUTHORITY, "notesGroup", NotesGroup);
sUriMatcher.addURI(NotePad.AUTHORITY, "notesGroup/#", NotesGroup_ID);2、在CRUD操作代码(根据匹配项分别操作两张表)
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
String sortOrder) {
// Constructs a new query builder and sets its table name
SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
String orderBy = null;
switch (sUriMatcher.match(uri)) {
// If the incoming URI is for notes, chooses the Notes projection
case NOTES:
qb.setTables(NotePad.Notes.TABLE_NAME);
qb.setProjectionMap(sNotesProjectionMap);
// If no sort order is specified, uses the default
if (TextUtils.isEmpty(sortOrder)) {
orderBy = NotePad.Notes.DEFAULT_SORT_ORDER;
} else {
// otherwise, uses the incoming sort order
orderBy = sortOrder;
}
break;
case NOTE_ID:
qb.setTables(NotePad.Notes.TABLE_NAME);
qb.setProjectionMap(sNotesProjectionMap);
qb.appendWhere(
NotePad.Notes._ID + // the name of the ID column
"=" +
uri.getPathSegments().get(NotePad.Notes.NOTE_ID_PATH_POSITION));
if (TextUtils.isEmpty(sortOrder)) {
orderBy = NotePad.Notes.DEFAULT_SORT_ORDER;
} else {
// otherwise, uses the incoming sort order
orderBy = sortOrder;
}
break;
//=====================================
case NotesGroup:
qb.setTables(NotePad.NotesGroup.TABLE_NAME);
qb.setProjectionMap(sGroupProjectionMap);
break;
case NotesGroup_ID:
qb.setTables(NotePad.NotesGroup.TABLE_NAME);
qb.appendWhere(NotePad.NotesGroup._ID + "=" + uri.getPathSegments().get(NotePad.NotesGroup.NOTE_ID_PATH_POSITION));
break;
default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
SQLiteDatabase db = mOpenHelper.getReadableDatabase();
Cursor c = qb.query(
db, // The database to query
projection, // The columns to return from the query
selection, // The columns for the where clause
selectionArgs, // The values for the where clause
null, // don't group the rows
null, // don't filter by row groups
orderBy // The sort order
);
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
}NotePadProvider类代码，代码中只给出query方法，其他操作方法按照同样思路写
NotePadProvider.java
public class NotePadProvider extends ContentProvider implements PipeDataWriter<Cursor> {
private static final String TAG = "NotePadProvider";
private static final String DATABASE_NAME = "note_pad.db";
private static final int DATABASE_VERSION = 2;
private static HashMap<String, String> sNotesProjectionMap;
private static HashMap<String,String> sGroupProjectionMap;
private static final String[] READ_NOTE_PROJECTION = new String[] {
NotePad.Notes._ID, // Projection position 0, the note's id
NotePad.Notes.COLUMN_NAME_NOTE, // Projection position 1, the note's content
NotePad.Notes.COLUMN_NAME_TITLE, // Projection position 2, the note's title
};
private static final int READ_NOTE_NOTE_INDEX = 1;
private static final int READ_NOTE_TITLE_INDEX = 2;
private static final String[] READ_GROUP_PROJECTION = new String[]{
NotePad.NotesGroup._ID,
NotePad.NotesGroup.COLUMN_NAME_GROUPTITLE
};
private static final int READ_GROUP_GROUPTITLE_INDEX = 1;
private static final int NOTES = 1;
private static final int NOTE_ID = 2;
private static final int NotesGroup = 4;
private static final int NotesGroup_ID = 5;
private static final UriMatcher sUriMatcher;
// Handle to a new DatabaseHelper.
private DatabaseHelper mOpenHelper;
static {
// Create a new instance
sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
// Add a pattern that routes URIs terminated with "notes" to a NOTES operation
sUriMatcher.addURI(NotePad.AUTHORITY, "notes", NOTES);
// Add a pattern that routes URIs terminated with "notes" plus an integer
// to a note ID operation
sUriMatcher.addURI(NotePad.AUTHORITY, "notes/#", NOTE_ID);
sUriMatcher.addURI(NotePad.AUTHORITY, "notesGroup", NotesGroup);
sUriMatcher.addURI(NotePad.AUTHORITY, "notesGroup/#", NotesGroup_ID);
sNotesProjectionMap = new HashMap<String, String>();
// Maps the string "_ID" to the column name "_ID"
sNotesProjectionMap.put(NotePad.Notes._ID, NotePad.Notes._ID);
// Maps "title" to "title"
sNotesProjectionMap.put(NotePad.Notes.COLUMN_NAME_TITLE, NotePad.Notes.COLUMN_NAME_TITLE);
// Maps "note" to "note"
sNotesProjectionMap.put(NotePad.Notes.COLUMN_NAME_NOTE, NotePad.Notes.COLUMN_NAME_NOTE);
// Maps "created" to "created"
sNotesProjectionMap.put(NotePad.Notes.COLUMN_NAME_CREATE_DATE,
NotePad.Notes.COLUMN_NAME_CREATE_DATE);
// Maps "modified" to "modified"
sNotesProjectionMap.put(
NotePad.Notes.COLUMN_NAME_MODIFICATION_DATE,
NotePad.Notes.COLUMN_NAME_MODIFICATION_DATE);
sNotesProjectionMap.put(NotePad.Notes.COLUMN_NAME_GROUPID,NotePad.Notes.COLUMN_NAME_GROUPID);
sGroupProjectionMap = new HashMap<String, String>();
sGroupProjectionMap.put(NotePad.NotesGroup._ID,NotePad.NotesGroup._ID);
sGroupProjectionMap.put(NotePad.NotesGroup.COLUMN_NAME_GROUPTITLE,NotePad.NotesGroup.COLUMN_NAME_GROUPTITLE);
}
/** * * This class helps open, create, and upgrade the database file. Set to package visibility * for testing purposes. */
static class DatabaseHelper extends SQLiteOpenHelper {
DatabaseHelper(Context context) {
// calls the super constructor, requesting the default cursor factory.
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE " + NotePad.Notes.TABLE_NAME + " ("
+ NotePad.Notes._ID + " INTEGER PRIMARY KEY,"
+ NotePad.Notes.COLUMN_NAME_TITLE + " TEXT,"
+ NotePad.Notes.COLUMN_NAME_NOTE + " TEXT,"
+ NotePad.Notes.COLUMN_NAME_CREATE_DATE + " INTEGER,"
+ NotePad.Notes.COLUMN_NAME_MODIFICATION_DATE + " INTEGER,"
+ NotePad.Notes.COLUMN_NAME_GROUPID + " INTEGER"
+ ");");
db.execSQL("CREATE TABLE " + NotePad.NotesGroup.TABLE_NAME +" ("
+ NotePad.NotesGroup._ID + " INTEGER PRIMARY KEY,"
+ NotePad.NotesGroup.COLUMN_NAME_GROUPTITLE + " TEXT"
+ ");"
);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Logs that the database is being upgraded
Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
+ newVersion + ", which will destroy all old data");
// Kills the table and existing data
db.execSQL("DROP TABLE IF EXISTS notes");
db.execSQL("DROP TABLE IF EXISTS notesGroup");
// Recreates the database with a new version
onCreate(db);
}
}
@Override
public boolean onCreate() {
// Creates a new helper object. Note that the database itself isn't opened until
// something tries to access it, and it's only created if it doesn't already exist.
mOpenHelper = new DatabaseHelper(getContext());
// Assumes that any failures will be reported by a thrown exception.
return true;
}
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
String sortOrder) {
// Constructs a new query builder and sets its table name
SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
String orderBy = null;
switch (sUriMatcher.match(uri)) {
// If the incoming URI is for notes, chooses the Notes projection
case NOTES:
qb.setTables(NotePad.Notes.TABLE_NAME);
qb.setProjectionMap(sNotesProjectionMap);
// If no sort order is specified, uses the default
if (TextUtils.isEmpty(sortOrder)) {
orderBy = NotePad.Notes.DEFAULT_SORT_ORDER;
} else {
// otherwise, uses the incoming sort order
orderBy = sortOrder;
}
break;
/* If the incoming URI is for a single note identified by its ID, chooses the * note ID projection, and appends "_ID = <noteID>" to the where clause, so that * it selects that single note */
case NOTE_ID:
qb.setTables(NotePad.Notes.TABLE_NAME);
qb.setProjectionMap(sNotesProjectionMap);
qb.appendWhere(
NotePad.Notes._ID + // the name of the ID column
"=" +
// the position of the note ID itself in the incoming URI
uri.getPathSegments().get(NotePad.Notes.NOTE_ID_PATH_POSITION));
// If no sort order is specified, uses the default
if (TextUtils.isEmpty(sortOrder)) {
orderBy = NotePad.Notes.DEFAULT_SORT_ORDER;
} else {
// otherwise, uses the incoming sort order
orderBy = sortOrder;
}
break;
//=====================================
case NotesGroup:
qb.setTables(NotePad.NotesGroup.TABLE_NAME);
qb.setProjectionMap(sGroupProjectionMap);
break;
case NotesGroup_ID:
qb.setTables(NotePad.NotesGroup.TABLE_NAME);
qb.appendWhere(NotePad.NotesGroup._ID + "=" + uri.getPathSegments().get(NotePad.NotesGroup.NOTE_ID_PATH_POSITION));
break;
//=======================================
case LIVE_FOLDER_NOTES:
// If the incoming URI is from a live folder, chooses the live folder projection.
qb.setProjectionMap(sLiveFolderProjectionMap);
break;
default:
// If the URI doesn't match any of the known patterns, throw an exception.
throw new IllegalArgumentException("Unknown URI " + uri);
}
// Opens the database object in "read" mode, since no writes need to be done.
SQLiteDatabase db = mOpenHelper.getReadableDatabase();
/* * Performs the query. If no problems occur trying to read the database, then a Cursor * object is returned; otherwise, the cursor variable contains null. If no records were * selected, then the Cursor object is empty, and Cursor.getCount() returns 0. */
Cursor c = qb.query(
db, // The database to query
projection, // The columns to return from the query
selection, // The columns for the where clause
selectionArgs, // The values for the where clause
null, // don't group the rows
null, // don't filter by row groups
orderBy // The sort order
);
// Tells the Cursor what URI to watch, so it knows when its source data changes
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
}
DatabaseHelper getOpenHelperForTest() {
return mOpenHelper;
}
}通过这种方法就可以实现使用一个ContentProvider来操作多张表，什么时候使用一个ContentProvider什么时候使用多个呢？像我呢，开发时不想多写一个ContentProvider就想到这个方法，其实看个人习惯吧。但如果数据库表中表数量变化，最好还是分开写好一点。
作者：陈伟杰：原文地址