将SQL查询分解为多个部分以访问内容提供程序

Question

我有一个来自字符串的SQL查询，正在尝试访问ContentProvider。sql查询看起来像：

String query = "SELECT * FROM application_settings WHERE _id = ?";

我必须通过获取ContentResolver来访问内容提供商，如：

context.getContentResolver().query()

但查询方法接受：

Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder);

有没有一种方法可以将字符串查询拆分为投影、选择、选择Args和排序顺序？

我不希望执行原始查询，所以我更希望有一个带绑定值的函数解决方案。

Answer 1

我刚刚编写了一个库，它提供了您需要的东西。你只需要将它复制并粘贴到项目中，如果你想根据你的需求添加、扩展和自定义它。

SqliteHandler.java

import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.util.Log;
class SqliteHandler {
// VERY IMPORTANT MAKE SURE IT'S CORRECT AND REGISTERED IN THE MANIFEST
private String PROVIDER_NAME = "com.example.android.mySqlite";
private String CONTENT_URL = "content://" + PROVIDER_NAME + "/";
private Context context;
SqliteHandler(Context context, String PROVIDER_NAME) {
this.context = context;
this.PROVIDER_NAME = PROVIDER_NAME;
}
Cursor exeQuery(String query) {
try {
queryObject obj = convertQueryStringToQueryObject(query);
return context.getContentResolver().query(obj.uri, obj.projection, obj.selection, obj.selectionArgs, null);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
Cursor exeQuery(String query, String[] selectionArgs) {
try {
queryObject obj = convertQueryStringToQueryObject(query);
return context.getContentResolver().query(obj.uri, obj.projection, obj.selection, selectionArgs, null);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
Cursor exeQuery(String query, String selection, String[] selectionArgs) {
try {
queryObject obj = convertQueryStringToQueryObject(query);
return context.getContentResolver().query(obj.uri, obj.projection, selection, selectionArgs, null);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
Cursor exeQuery(String query, String[] projection, String[] selectionArgs) {
try {
queryObject obj = convertQueryStringToQueryObject(query);
return context.getContentResolver().query(obj.uri, projection, obj.selection, selectionArgs, null);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
Cursor exeQuery(queryObject obj) {
try {
return context.getContentResolver().query(obj.uri, obj.projection, obj.selection, obj.selectionArgs, null);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}

class queryObject {
Uri uri;
String[] projection;
String selection;
String[] selectionArgs;
String sortOrder;
queryObject(String table_name, String[] projection, String selection, String[]
selectionArgs) {
this.uri = Uri.parse(CONTENT_URL + table_name);
this.projection = projection;
this.selection = selection;
this.selectionArgs = selectionArgs;
}
}
queryObject convertQueryStringToQueryObject(String query) {
try {
String selection = null;
String[] selectionArgs = null;
query = query.toLowerCase();
String[] s = query.split("select")[1].split("from");
String[] projection = s[0].split(",");
String[] s2 = s[1].split("where");
String table_name = s2[0];
String logText = "";
if (s2.length > 1) {
selection = s2[1];
String[] args = s2[1].split("=");
selectionArgs = new String[args.length - 1];// half of the args are values others are keys
int count = 0;
for (int i = 1; i < args.length; i++) {
selectionArgs[count] = args[i]
.split("and")[0]
.split("or")[0]
.replace(" ", "")
.replace("and", "")
.replace("or", "");
count++;
}
for (int i = 0; i < selectionArgs.length; i++) {
logText += selectionArgs[i];
if (i < selectionArgs.length - 1) logText += ",";
selection = selection.replace(selectionArgs[i], "?");
}
}
Log.i("table_name", table_name);
Log.i("selection: ", selection == null ? "null" : selection);
Log.i("selectionArgs", logText.equals("") ? "null" : logText);
logText = "";
for (int i = 0; i < projection.length; i++) {
logText += projection[i];
if (i < projection.length - 1) logText += ",";
}
Log.i("projection", logText);
return new queryObject(table_name, projection, selection, selectionArgs);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}}

如何使用

实例化SqliteHandler，传递有效的PROVIDER_NAME以及确保您的CONTENT_PROVIDER已在AndroidManiFest.xml中注册是非常重要的。为了说明它是如何工作的，我们传递了三个不同的查询，并获得了类型为queryObject的对象的返回值

SqliteHandler sh = new SqliteHandler(this,"PROVIDER_NAME");
SqliteHandler.queryObject obj1 = sh.convertQueryStringToQueryObject("SELECT * FROM table_name");
SqliteHandler.queryObject obj2 = sh.convertQueryStringToQueryObject("SELECT * FROM table_name WHERE _id = ?");
SqliteHandler.queryObject obj3 = sh.convertQueryStringToQueryObject("SELECT param1,param2,param3 FROM table_name WHERE param1 ="a" and param2="b" or param3="c"");

方法convertQueryStringToQueryObject将query string转换为query class，然后我们可以将该类用于getContentResolver().query()。

---

重要提示：因为getContentResolver().query()需要Uri。因此，我们需要从table_name创建一个Uri。因此，我们需要将有效的PROVIDER_NAME传递给SqliteHandler的实例。

---

输出日志

正如您所看到的，三个不同的查询被分解为参数，我们可以在getContentResolver().query()中使用这些参数

// 1th query 
I/table_name:  table_name
I/selection:: null
I/selectionArgs: null
I/projection:  * 
// 2th query 
I/table_name:  table_name 
I/selection::  _id = ?
I/selectionArgs: ?
I/projection:  * 
// 3th query 
I/table_name:  table_name 
I/selection::  param1 =? and param2=? or param3=?
I/selectionArgs: "a","b","c"
I/projection:  param1,param2,param3 

完整示例

在CCD_ 19中存在具有若干过载的CCD_ 20方法。此外，根据不同的输入参数，您可以在Content Provider处设置Cursor。

SqliteHandler sh = new SqliteHandler(this,"PROVIDER_NAME");
SqliteHandler.queryObject obj1 = sh.convertQueryStringToQueryObject("SELECT * FROM table_name");
SqliteHandler.queryObject obj2 = sh.convertQueryStringToQueryObject("SELECT * FROM table_name WHERE _id = ?");
SqliteHandler.queryObject obj3 = sh.convertQueryStringToQueryObject("SELECT param1,param2,param3 FROM table_name WHERE param1 ="a" and param2="b" or param3="c"");
Cursor c = sh.exeQuery(obj1);
Cursor c = sh.exeQuery(obj2);
Cursor c = sh.exeQuery(obj3);
Cursor c = sh.exeQuery("SELECT param1,param2,param3 FROM table_name WHERE param1 ="a" and param2="b" or param3="c"");
Cursor c = sh.exeQuery("SELECT * FROM table_name WHERE _id = ?",new String[]{"whereArg"});
Cursor c = sh.exeQuery("SELECT * FROM table_name"," _id = ? ",new String[]{"whereArg"});
Cursor c = sh.exeQuery("SELECT ? FROM table_name WHERE _id = ?",new String[]{"Field"},new String[]{"whereArg"});

但是，如果您不想使用exeQuery，请尝试以下步骤：

queryObject obj = convertQueryStringToQueryObject(query);
Cursor c = this.getContentResolver().query(obj.uri, obj.projection, obj.selection, obj.selectionArgs, null);

Answer 2

https://developer.android.com/guide/topics/providers/content-provider-basics#ClientProvider

cursor = getContentResolver().query(
UserDictionary.Words.CONTENT_URI,   // The content URI of the words table
projection,                        // The columns to return for each row
selectionClause,                   // Selection criteria
selectionArgs,                     // Selection criteria
sortOrder);                        // The sort order for the returned rows

您可以执行此

String[] projection = {"*"};
String[] selectionArgs = {"1", "2"}; //your ids here
Cursor cursor = getContentResolver().query(Uri.parse("content://your_provider/your_table"), projection, "_id", selectionArgs, null);
cursor.close();

要创建提供程序，请查看以下内容https://developer.android.com/guide/topics/providers/content-provider-creating#top_of_page

另请参阅此答案https://stackoverflow.com/a/1031101/10989990