I am trying to retrieve an integer from my SQLite database and my current query crashes my program. This is what I have so far:
*/
public int getWin(String id){
SQLiteDatabase db = this.getWritableDatabase();
String query = "SELECT " + COL3 + " FROM " + TABLE_NAME +
" WHERE " + COL2 + " = '" + id + "'";
Log.d(TAG, "updateName: query: " + query);
db.execSQL(query);
int win = Integer.parseInt(query);
return win;
}
I am not sure why this will not work. Thanks in advance.
You are trying to convert the value SELECT ......... into a number as per int win = Integer.parseInt(query);.
For a SELECT statment you need you need to retrieve a Cursor (result set), via either the query or rawQuery SQLiteDatabase method and then extract the value(s) from the method and to then access the respective column from the respective row(s).
I believe that you would use something like :-
public int getWin(String id){
SQLiteDatabase db = this.getWritableDatabase();
int rv = -1; //<<<<<<<<<< ADDED default value to return if no row found
String query = "SELECT " + COL3 + " FROM " + TABLE_NAME +
" WHERE " + COL2 + " = '" + id + "'";
Log.d(TAG, "updateName: query: " + query);
Cursor csr = db.rawQuery(query,null); //<<<<<<<<<< CHANGED to get the Cursor returned
// ADDED the following IF construct
if (csr.moveToFirst()) {
rv = csr.getInt(csr.getColumnIndex(COL3));
}
//int win = Integer.parseInt(query); //<<<<<<<<<< DELETED (commented out)
csr.close(); //<<<<<<<<<< ADDED should always close a Cursor when done with it
return rv; //<<<<<<<<<< return the value (-1 if no row found)
}
This assumes that you just want the value from a single row as identified by the WHERE clause.
If possible it is recommended to a) not build the query with direct values (makes it vulnerable to SQL Injection) and to b) utilise the convenience query method.
Apply both a and b and your code could be :-
public int getWin(String id){
SQLiteDatabase db = this.getWritableDatabase();
int rv = -1;
String whereclause = COL2 + "=?"; //<<<<<<<<<< where clause without where and ? for value that will be passed
String[] whereargs = new String[]{String.valueOf(id)}; //<<<<<<<<<< arguments used by the whereclause ? replaced on a 1 for 1 basis
String[] columns = new String[]{COL3}; //<<<<<<<<<< the columns to extract as a String array
Cursor csr = db.query(TABLE_NAME,columns,whereclause,whereargs,null,null,null);
if (csr.moveToFirst()) {
rv = csr.getInt(csr.getColumnIndex(COL3));
}
csr.close();
return rv;
}
I am working on a student grade submission program that accepts the following inputs: Student ID, Student First Name, Student Last Name, Class ID, Class Name, Grade Points, and Letter Grade. In order to prevent data redundancy I have created three different tables. However when attempting to "modify" or "delete" an entry with two values from distinct tables I am running into a problem. (For instance delete WHERE student.id is equal to the student.id in STUDENT_TABLE and WHERE class.id is equal to the class.id in the CLASS_TABLE)
With that being said, here is my current Modify code for Modifying a Student Class. I need to modify in a way in which the student.id and class.id are associated (Which are Located in two different Tables)
modifyclass.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
if(studentid.getText().toString().trim().length()==0 || classid.getText().toString().trim().length()==0 || classname.getText().toString().trim().length()==0)
{
showMessage("Error", "Please enter Student & Class ID to update class. \n\nAll other Field Entries will be ignored");
return;
}
Cursor c=db.rawQuery("SELECT * FROM CLASS_TABLE WHERE classid='"+classid.getText()+"'", null);
if(c.moveToFirst())
{
db.execSQL("UPDATE CLASS_TABLE SET classid='"+classid.getText()+"',classname='"+classname.getText()+"' WHERE studentid='"+studentid.getText()+"' AND classid='"+classid.getText()+"'");
showMessage("Success", "Class Record Modified");
}
else
{
showMessage("Error", "Invalid First and Last name or Class ID");
}
clearText();
}
});
EDIT:
Here are my tables for reference:
db=openOrCreateDatabase("STUDENTGRADES", Context.MODE_PRIVATE, null);
db.execSQL("CREATE TABLE IF NOT EXISTS STUDENT_TABLE (studentid TEXT, fname TEXT, lname TEXT)");
db.execSQL("CREATE TABLE IF NOT EXISTS CLASS_TABLE(classid TEXT PRIMARY KEY, classname TEXT UNIQUE)");
db.execSQL("CREATE TABLE IF NOT EXISTS GRADE_TABLE (studentid TEXT, classid TEXT, pointgrade INTEGER, lettergrade TEXT)");
You should never need to update multiple tables at once at least for a single change e.g. student's name has changed (student table would be changed) or say a grade changed (change the student's respective grade entry).
So I believe what would best suit are methods to update a Student's details (first or last name or both) and a method to alter the grades (again either or both).
As for deletion you could do this sequentially delete from the grades table and the from the student table or vice-versa.
As such I believe the following code includes methods deleteStudentInfo, changeStudentName, changeStudentFirstName, changeStudentLastName and changeStudentGrade and also includes example usage along with creating and populating the tables (you may wish to consider the revised schema):-
public class MainActivity extends AppCompatActivity {
public static final String DBNAME = "study";
public static final String STUDENT_TABLE_NAME = "STUDENT_TABLE";
public static final String COL_STUDENT_ID = "studentid";
public static final String COL_STUDENT_FIRSTNAME = "fname";
public static final String COL_STUDENT_LASTNAME = "lname";
public static final String CLASS_TABLE_NAME = "CLASS_TABLE";
public static final String COL_CLASS_ID = "classid";
public static final String COL_CLASS_NAME = "classname";
public static final String GRADE_TABLE_NAME = "GRADE_TABLE";
public static final String COL_GRADE_POINTGRADE = "pointgrade";
public static final String COL_GRADE_LETTERGRADE = "lettergrade";
public static final String BY_STUDENTID = COL_STUDENT_ID + "=?";
public static final String BY_CLASSID = COL_CLASS_ID + "=?";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SQLiteDatabase db = openOrCreateDatabase(DBNAME,Context.MODE_PRIVATE,null);
db.execSQL("CREATE TABLE IF NOT EXISTS " + STUDENT_TABLE_NAME + " (" +
COL_STUDENT_ID + " TEXT PRIMARY KEY, " +
COL_STUDENT_FIRSTNAME + " TEXT," +
COL_STUDENT_LASTNAME + " TEXT)"
);
db.execSQL("CREATE TABLE IF NOT EXISTS " + CLASS_TABLE_NAME + "(" +
COL_CLASS_ID + " TEXT PRIMARY KEY," +
COL_CLASS_NAME + " TEXT UNIQUE " +
")"
);
db.execSQL("CREATE TABLE IF NOT EXISTS " + GRADE_TABLE_NAME + "(" +
COL_STUDENT_ID + " TEXT, " +
COL_CLASS_ID + " TEXT, " +
COL_GRADE_POINTGRADE + " INTEGER, " +
COL_GRADE_LETTERGRADE + " TEXT" +
")"
);
db.execSQL("INSERT OR IGNORE INTO " + STUDENT_TABLE_NAME +
" VALUES" +
"('00001','Fred','Smith')," +
"('00010','Mary','Thomas')," +
"('00910','Angela','Jones')"
);
db.execSQL("INSERT OR IGNORE INTO " + CLASS_TABLE_NAME +
" VALUES" +
"('001','English')," +
"('101','Mathematics')," +
"('201','Chemistry')"
);
db.execSQL("INSERT OR IGNORE INTO " + GRADE_TABLE_NAME +
" VALUES" +
" ('00001','001',99,'A'), -- Fred Smith has 99 point grade as an A in English\n" +
" ('00001','101',25,'F'), -- Fred Smith has 25 point grade as an F on Mathematics\n" +
" ('00010','201',76,'B'), -- Angela Jones 76 a B in Chemistry\n" +
" ('00910','101',50,'C'), \n" +
" ('00910','201',63,'C'),\n" +
" ('00910','001',89,'A')\n" +
";"
);
changeStudentName(db,"00001","Joe","Bloggs");
changeStudentFirstName(db,"00001","Harry");
changeStudentLastName(db,"00001","Hoffmann");
// e.g. won't change due to -1 (skip pointsgrade) and null (skip lettergrade)
changeStudentGrade(db,"00001","001",-1,null);
// Change both
changeStudentGrade(db,"00001","001",25,"D");
changeStudentGrade(db,"00001","001",27,null);
// Ooops invalid student id
if (deleteStudentInfo(db,"001")) {
Log.d("DELETION","Student 001 deleted.");
} else {
Log.d("DELETION","Ooops Student 001 not deleted?????");
}
// Corrected Student ID
if (deleteStudentInfo(db,"00001")) {
Log.d("DELETION","Student 001 deleted.");
} else {
Log.d("DELETION","Ooops Student 001 not deleted?????");
}
}
private boolean deleteStudentInfo(SQLiteDatabase db, String studentid) {
String tag = "STUDENT_DELETE";
String student_table = "STUDENT_TABLE";
String grade_table = "GRADE_TABLE";
long pre_delete_student_count = DatabaseUtils.queryNumEntries(db,student_table);
long pre_delete_grade_count = DatabaseUtils.queryNumEntries(db,grade_table);
String whereclause = "studentid =?";
String[] whereargs = {studentid};
db.delete(student_table,whereclause,whereargs);
db.delete(grade_table,whereclause,whereargs);
long post_delete_student_count = DatabaseUtils.queryNumEntries(db,student_table);
long post_delete_grade_count = DatabaseUtils.queryNumEntries(db,grade_table);
Log.d(
tag,
"Number of Students deleted from " +
student_table + " is " +
String.valueOf(
pre_delete_student_count - post_delete_student_count
));
Log.d(
tag,
"Number of Grades deleted from " + grade_table + " is " +
String.valueOf(
pre_delete_grade_count - post_delete_grade_count
)
);
if ((pre_delete_student_count + pre_delete_grade_count) != (post_delete_student_count + post_delete_grade_count)) {
return true;
}
return false;
}
/**
* Flexible Student Name Change
*
* #param db The SQliteDatabase
* #param studentid The studentid (String)
* #param newfirstname The new firstname, null or blank to leave as is
* #param newlastname the new lastname, null or blank to leave as is
*/
private void changeStudentName(SQLiteDatabase db, String studentid, String newfirstname, String newlastname ) {
//Anything to do? if not do nothing
if ((newfirstname == null || newfirstname.length() < 1) && (newlastname == null || newlastname.length() < 1)) {
return;
}
ContentValues cv = new ContentValues();
if (newfirstname != null && newfirstname.length() > 0) {
cv.put(COL_STUDENT_FIRSTNAME,newfirstname);
}
if (newlastname != null && newlastname.length() > 0) {
cv.put(COL_STUDENT_LASTNAME,newlastname);
}
// Overcautious check
if (cv.size() < 1) {
return;
}
db.update(STUDENT_TABLE_NAME,cv,BY_STUDENTID,new String[]{studentid});
}
/**
* Change a Student's First Name (invokes changeStudentName method)
* #param db The SQLiteDatabase
* #param studentid The student's id (String)
* #param newfirstname The new first name to apply
*/
private void changeStudentFirstName(SQLiteDatabase db, String studentid, String newfirstname) {
changeStudentName(db,studentid,newfirstname,null);
}
/**
* Change a Student's Last Name (invokes changeStudentName method)
* #param db
* #param studentid
* #param newlastname
*/
private void changeStudentLastName(SQLiteDatabase db, String studentid, String newlastname) {
changeStudentName(db,studentid,null,newlastname);
}
/**
* Change a students grade (allowing just one (points/letter))
* #param db
* #param studentid
* #param classid
* #param newpointsgrade
* #param newlettergrade
*/
private void changeStudentGrade(SQLiteDatabase db, String studentid, String classid, int newpointsgrade, String newlettergrade) {
// Anything to do? if not do nothing
if (newpointsgrade < 0 && (newlettergrade == null || newlettergrade.length() < 1)) {
return;
}
ContentValues cv = new ContentValues();
if (newpointsgrade >= 0) {
cv.put(COL_GRADE_POINTGRADE,newpointsgrade);
}
if (newlettergrade != null && newlettergrade.length() > 0) {
cv.put(COL_GRADE_LETTERGRADE,newlettergrade);
}
String whereclause = COL_STUDENT_ID + "=? AND " + COL_CLASS_ID + "=?";
String[] whereargs = new String[]{studentid,classid};
db.update(GRADE_TABLE_NAME,cv,whereclause,whereargs);
}
}
Hi, I have some problem to fetch data from sqlite database. Here i am fetching
data from select query but it is not responding. Please help me.
public ArrayList<String> getStudentsByClass(String stud_info) {
// Log.i("SKR", "GETTING STUDENTS by " +stud_class);
ArrayList<String> arrayList = new ArrayList<>();
Cursor cursor = liteDatabase.rawQuery("SELECT * FROM " + DATABASE_TABLE2 +
" WHERE ssg ='" + stud_info + "'", null);
if (cursor != null) {
cursor.moveToFirst();
while (cursor.isAfterLast() == false) {
arrayList.add(cursor.getString(cursor.getColumnIndex(KEY_STUDENT_NAME)));
cursor.moveToNext();
}
}
}
return arrayList;
}
Here is a raw query from a DBHelper Class that when called populates an ArrayList
/* Retrive ALL data from database table named "TABLE_INFO" */
public List<DatabaseModel> getDataFromDB(){
List<DatabaseModel> modelList = new ArrayList<>();
String query = "SELECT * FROM " + TABLE_INFO;
//String query = "SELECT * FROM " + TABLE_INFO + " WHERE " + Col_ID + " > 0 " + " ORDER BY " + Col_ID + " DESC ";
/* Notice the SPACES before AND after the words WHERE ORDER BY ASC or DESC most of all the condition " > 0 "*/
/* =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=*/
db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(query,null);
if (cursor.moveToFirst()){
do {
DatabaseModel model = new DatabaseModel();
model.setID(cursor.getString(0));
model.setWebsite(cursor.getString(1));
model.setUsernane(cursor.getString(2));
model.setPassword(cursor.getString(3));
model.setQuestion(cursor.getString(4));
model.setAnswer(cursor.getString(5));
model.setNotes(cursor.getString(6));
modelList.add(model);
}while (cursor.moveToNext());
}
db.close();
return modelList;
}
using rawQuery You may include ?s in where clause in the query, which will be replaced by the values from selectionArgs. The values will be bound as Strings.
String selectQuery = "select * FROM settings where _id = ?";
String args[] = {"1"};
Cursor c = db.rawQuery(selectQuery, args);
if (c.moveToFirst()) {
I have to bind an <asp:calendar> with data fetched from a database using a linq query.
Here is the linq code
public List<AllCalander> SearchCalender(int month, int zip, string type, int cause)
{
var xyz = (from m in DB.Calenders
where(m.DateFrom.Value.Month==month || m.Zip==zip || m.ActivityType==type || m.CauseID==cause)
group m by new { m.DateFrom } into grp
select new
{
caustitle = grp.Select(x => x.Caus.CauseTitle),
datfrm = grp.Key.DateFrom,
total = grp.Count()
})
.ToList()
.Select(m => new AllCalander
{
DateFrom =Convert.ToDateTime(m.datfrm),
CauseTitle = string.Join(",", m.caustitle),
Total = m.total
});
My aspx.cs code is here
List<AllCalander> calnder = calbll.SearchCalender(mnth,ZipString,type,causeString);
foreach (var myItem in calnder)
{
string datetime = myItem.DateFrom.ToString();
Literal myEventNameLiteral = new Literal();
myEventNameLiteral.ID = i + myItem.CauseID.ToString();
// string currentcalanderDate = e.Day.Date.Day.ToString() ;
if (string.Equals(DateTime.Parse(datetime).ToString("MMM dd yyyy"), e.Day.Date.ToString("MMM dd yyyy")))
{
string a = myItem.CauseTitle;
if (a != cause)
cause = a;
coun++;
myEventNameLiteral.Mode = LiteralMode.PassThrough;
myEventNameLiteral.Text = "<br /><span style='font-family:verdana; font-size:10px;'>" + myItem.CauseTitle + "(" + myItem.Total + ")"+ " ";
e.Cell.Controls.Add(myEventNameLiteral);
}
i++;
}
but on output it only shows the last value from database instead of showing all the data.
Can somebody please tell me what's wrong?
Thanks in advance
group m by new { m.DateFrom, m.Caus.CauseTitle } into grp
string companyName="ABC";
var query = from q in context.Company where q.CompanyName == companyName select q;
Is there any way to replace the q.CompanyName part of the query with a string variable
so that the field used for filtering be a parametric?
I tried
string str1 = "companySize";
string str2 = "q." + str1;
string companySize = "Mid";
var query = from q in context.Company where str2 == companySize select q;
Didn't work.
Been trying to let the user choose the columns for the query.
Read more about both below option at : Dynamic query with Linq
you can use one of this
Use Dynamic LINQ library
Example for the the blog below
string strWhere = string.Empty;
string strOrderBy = string.Empty;
if (!string.IsNullOrEmpty(txtAddress.Text))
strWhere = "Address.StartsWith(\"" + txtAddress.Text + "\")";
if (!string.IsNullOrEmpty(txtEmpId.Text))
{
if(!string.IsNullOrEmpty(strWhere ))
strWhere = " And ";
strWhere = "Id = " + txtEmpId.Text;
}
if (!string.IsNullOrEmpty(txtDesc.Text))
{
if (!string.IsNullOrEmpty(strWhere))
strWhere = " And ";
strWhere = "Desc.StartsWith(\"" + txtDesc.Text + "\")";
}
if (!string.IsNullOrEmpty(txtName.Text))
{
if (!string.IsNullOrEmpty(strWhere))
strWhere = " And ";
strWhere = "Name.StartsWith(\"" + txtName.Text + "\")";
}
EmployeeDataContext edb = new EmployeeDataContext();
var emp = edb.Employees.Where(strWhere);
Predicate Builder
EXample
var predicate = PredicateBuilder.True<employee>();
if(!string.IsNullOrEmpty(txtAddress.Text))
predicate = predicate.And(e1 => e1.Address.Contains(txtAddress.Text));
if (!string.IsNullOrEmpty(txtEmpId.Text))
predicate = predicate.And(e1 => e1.Id == Convert.ToInt32(txtEmpId.Text));
if (!string.IsNullOrEmpty(txtDesc.Text))
predicate = predicate.And(e1 => e1.Desc.Contains(txtDesc.Text));
if (!string.IsNullOrEmpty(txtName.Text))
predicate = predicate.And(e1 => e1.Name.Contains(txtName.Text));
EmployeeDataContext edb= new EmployeeDataContext();
var emp = edb.Employees.Where(predicate);
If you don't want to use libraries like dynamicLINQ, you can just create the Expression Tree by yourself:
string str1 = "companySize";
string str2 = "q." + str1;
string companySize = "Mid";
var param = Expression.Parameter(typeof(string));
var exp = Expression.Lambda<Func<Company, bool>>(
Expression.Equal(
Expression.Property(param, str1),
Expression.Constant(companySize)),
param);
var query = context.Company.Where(exp);
I think the best way to do this is with built in libraries (and PropertyDescriptor type).
using System.ComponentModel;
void Main()
{
Test test = new Test();
test.CompanyName = "ABC";
object z = TypeDescriptor.GetProperties(test).OfType<PropertyDescriptor>()
.Where(x => x.Name == "CompanyName").Select(x => x.GetValue(test)).FirstOrDefault();
Console.WriteLine(z.ToString());
}
public class Test
{
public string CompanyName { get; set; }
}