SQLite Data Insertion Issue: Partial Data Written Without Errors

Schema and Insertion Logic Overview

The core issue revolves around the insertion of data into an SQLite database where the application reports successful insertions, but only a portion of the data is actually written to the database. The schema in question involves two tables: Blasting_Record_Head and Blasting_Record_Detail. The Blasting_Record_Detail table has a foreign key relationship with the Blasting_Record_Head table, specifically referencing the id column. The insertion logic is implemented using Qt’s database interface, where a prepared statement is used to insert multiple rows into the Blasting_Record_Detail table.

The Blasting_Record_Detail table is defined as follows:

CREATE TABLE Blasting_Record_Detail (
    Head_id  INTEGER REFERENCES Blasting_Record_Head (id) ON DELETE NO ACTION ON UPDATE NO ACTION MATCH NONE,
    BurstTime INTEGER,
    uID    CHAR,
    Delay   INTEGER,
    Hole   INTEGER
);

The insertion logic is encapsulated in a function Insert_Blasting_Record_Replace, which iterates over a list of messages (LGMessage_List). For each message, it prepares an SQL INSERT statement, binds the necessary values, and executes the query. The function returns 0 if all insertions are successful and 1 if any insertion fails.

Possible Causes of Partial Data Insertion

The issue of partial data insertion without errors can be attributed to several potential causes, each of which needs to be carefully examined:

1. Transaction Management: SQLite operates in autocommit mode by default, meaning each INSERT statement is treated as a separate transaction. If the application does not explicitly manage transactions, partial data insertion can occur if the application crashes or is interrupted before all INSERT statements are executed. In this case, the data inserted before the interruption would be committed, while the remaining data would be lost.

2. Foreign Key Constraints: The Blasting_Record_Detail table has a foreign key constraint referencing the Blasting_Record_Head table. If the referenced id in the Blasting_Record_Head table does not exist, the insertion into Blasting_Record_Detail would fail silently if the application does not check for foreign key constraint violations. This could result in partial data insertion if some id values are valid while others are not.

3. Data Type Mismatches: The uID column in the Blasting_Record_Detail table is defined as CHAR. If the data being inserted into this column does not match the expected data type or length, SQLite may silently truncate or reject the data without raising an error. This could lead to partial data insertion if some rows contain valid uID values while others do not.

4. Concurrency Issues: If multiple threads or processes are accessing the database simultaneously, concurrency issues could arise. For example, if one process is inserting data while another process is modifying or deleting related data in the Blasting_Record_Head table, this could lead to inconsistent data insertion. SQLite’s locking mechanism may prevent some insertions from occurring, but this would typically result in an error rather than silent failure.

5. Application Logic Errors: The application logic may contain errors that prevent all insertions from being executed. For example, if the LGMessage_List contains fewer items than expected, or if the LG_ScanNumber variable is not correctly set, the function may return prematurely, resulting in partial data insertion.

6. Database Corruption: Although rare, database corruption could cause data to be partially written without raising an error. This could occur due to hardware issues, file system errors, or bugs in the SQLite library. In such cases, the database may need to be repaired or restored from a backup.

Troubleshooting Steps, Solutions & Fixes

To diagnose and resolve the issue of partial data insertion, the following troubleshooting steps and solutions should be implemented:

1. Explicit Transaction Management: Ensure that the application explicitly manages transactions when performing multiple insertions. This can be done by wrapping the insertion logic in a transaction block using BEGIN TRANSACTION and COMMIT statements. If any insertion fails, the entire transaction can be rolled back using ROLLBACK, ensuring that either all insertions are committed or none are.

   query->exec("BEGIN TRANSACTION");
   for (int i = 0; i < count; i++) {
       // Prepare and execute the INSERT statement
       if (!query->exec()) {
           query->exec("ROLLBACK");
           return 1; // fail
       }
   }
   query->exec("COMMIT");
   

2. Foreign Key Constraint Validation: Before inserting data into the Blasting_Record_Detail table, validate that the referenced id values exist in the Blasting_Record_Head table. This can be done by executing a SELECT query to check for the existence of each id before performing the insertion.

   QSqlQuery checkQuery;
   checkQuery.prepare("SELECT id FROM Blasting_Record_Head WHERE id = :Head_id");
   checkQuery.bindValue(":Head_id", id);
   if (!checkQuery.exec() || !checkQuery.next()) {
       // The referenced id does not exist
       return 1; // fail
   }
   

3. Data Type Validation: Ensure that the data being inserted into the uID column matches the expected data type and length. This can be done by validating the uID string before binding it to the query. If the uID string is too long or contains invalid characters, it should be rejected or truncated to the appropriate length.

   QString Str = QString("")
       .sprintf("%02x%02x%02x%02x%02x%02x%02x",
                _lgmagd_temp.Uid[0], _lgmagd_temp.Uid[1],
                _lgmagd_temp.Uid[2], _lgmagd_temp.Uid[3],
                _lgmagd_temp.Uid[4], _lgmagd_temp.Uid[5],
                _lgmagd_temp.Uid[6]);
   if (Str.length() > MAX_UID_LENGTH) {
       // The uID string is too long
       return 1; // fail
   }
   

4. Concurrency Control: If the application is multi-threaded or accessed by multiple processes, implement concurrency control mechanisms to prevent data inconsistencies. This can be done using SQLite’s BEGIN EXCLUSIVE TRANSACTION statement to lock the database during critical sections of code.

   query->exec("BEGIN EXCLUSIVE TRANSACTION");
   for (int i = 0; i < count; i++) {
       // Prepare and execute the INSERT statement
       if (!query->exec()) {
           query->exec("ROLLBACK");
           return 1; // fail
       }
   }
   query->exec("COMMIT");
   

5. Application Logic Review: Review the application logic to ensure that all necessary insertions are being executed. Verify that the LGMessage_List contains the expected number of items and that the LG_ScanNumber variable is correctly set. If the function returns prematurely, adjust the logic to ensure that all insertions are attempted.

6. Database Integrity Check: Perform a database integrity check to rule out corruption as a cause of the issue. This can be done using the PRAGMA integrity_check command, which will report any inconsistencies or corruption in the database.

   QSqlQuery integrityQuery;
   integrityQuery.exec("PRAGMA integrity_check");
   while (integrityQuery.next()) {
       QString result = integrityQuery.value(0).toString();
       if (result != "ok") {
           // Database corruption detected
           return 1; // fail
       }
   }
   

7. Error Logging and Debugging: Enhance error logging to capture more detailed information about the insertion process. Log the SQL statements being executed, the values being bound, and the results of each insertion. This will help identify any patterns or specific conditions under which the issue occurs.

   if (!query->exec()) {
       QString error = query->lastError().text();
       LOG_PRT("Insertion failed: %s\n", error.toUtf8().constData());
       return 1; // fail
   }
   

8. Database Backup and Restore: As a last resort, if database corruption is suspected, restore the database from a backup. Ensure that regular backups are taken to minimize data loss in the event of corruption.

By systematically addressing each of these potential causes and implementing the corresponding solutions, the issue of partial data insertion without errors can be effectively diagnosed and resolved. This approach ensures that the database remains consistent and that all data is correctly written, even in the face of unexpected conditions or errors.