Question

我有一个包含这些列的表：

import java.util.prefs.Preferences;

public class DataClass {

public void createPreference(String name, int value) {
    Preferences prefs = Preferences.userNodeForPackage(DataClass.class);
    if (prefs.getInt(name, -1) == -1) {
        prefs.putInt(name, value);
        System.out.println("Created For you, "+name+" with value: "+value);
    } else {
        System.out.println("Already Exist");
    }
}

public int readPreference(String name) {
    Preferences prefs = Preferences.userNodeForPackage(DataClass.class);
    return prefs.getInt(name, -1);
}

public void updatePreference(String name) {
    Preferences prefs = Preferences.userNodeForPackage(DataClass.class);
    int val = prefs.getInt(name, -1);
    if (val != -1) {
        val++;
        prefs.remove(name);
        prefs.putInt(name, val);
        System.out.println("New Value of "+name+" is: "+prefs.getInt(name, -1));
    }
}

public void removePreference(String key) {
    Preferences prefs = Preferences.userNodeForPackage(DataClass.class);
    if(prefs.getInt(key, -1) != -1){
        prefs.remove(key);
        System.out.println("Removed: "+key);
    }else{
        System.out.println("No Such Data in: "+key);
    }
}

}

我创建了一个跟随值的记录

id, exchange, name

然后我查询它，其中有na, "ted1", "ted1-curA"。

exchange=ted1

引发了database.query(true, "cur", null, null , null, "name","exchange=name1", null, null);

的异常

测试代码是

no such column name1

Answer 1

name1应该是单引号，例如＆＃34; exchange =＆＃39; name1＆＃39;＆＃34;

构建dataBases的最佳方法是在分离的类中使用常量请创建一个常量类，并将所有数据库常量放在那里：

public static final String DATA_BASE_NAME = "appStructure.db";
public static final int DATA_BASE_VERSION = 1;
public static final String TABLE_NAME = "Data_Table";
public static final String COLUMN_IDS = "_id";
public static final String COLUMN_TITLE = "Titles";
public static final String COLUMN_CONTENT = "Contents";
public static final String COLUMN_IMAGE = "Images";
public static final String COLUMN_LOCATION = "Location";

public static final String CREATE_DB_TABLE_COMMAND = "CREATE TABLE 
"+TABLE_NAME+"( "+COLUMN_ID+" INTEGER PRIMARY KEY AUTOINCREMENT, 
"+COLUMN_TITLE+" TEXT, "+COLUMN_CONTENT+" TEXT, "+COLUMN_IMAGE+" BLOB, 
"+COLUMN_LOCATION+" TEXT"+");";

并轻松地在项目中使用它们。

尝试查询sqlight时，查询方法查询会导致异常

1 个答案: