Getting table schema doesn't seem to work with System.Data.SQLite

问题

I'm using SQLite.NET to access my databases, and in one particular case, I need to get a table schema because it's application-specific.

I've been looking through the SQLite.NET forum and google, and it seems very straightforward. If I have a table called MYTABLE, I should be able to do this:

DataTable dt = Connection.GetSchema( SQLiteMetaDataCollectionNames.Columns, new string[] { null, null, "MYTABLE", null });

The problem is that, although I do get a DataTable back, it's got all of the wrong information in it. Specifically, this is what I get back for the supposed columns of MYTABLE:

[0] {TABLE_CATALOG} object {System.Data.DataColumn}
[1] {TABLE_SCHEMA} object {System.Data.DataColumn}
[2] {TABLE_NAME} object {System.Data.DataColumn}
[3] {COLUMN_NAME} object {System.Data.DataColumn}
[4] {COLUMN_GUID} object {System.Data.DataColumn}
[5] {COLUMN_PROPID} object {System.Data.DataColumn}
[6] {ORDINAL_POSITION} object {System.Data.DataColumn}
[7] {COLUMN_HASDEFAULT} object {System.Data.DataColumn}
[8] {COLUMN_DEFAULT} object {System.Data.DataColumn}
[9] {COLUMN_FLAGS} object {System.Data.DataColumn}
[10] {IS_NULLABLE} object {System.Data.DataColumn}
[11] {DATA_TYPE} object {System.Data.DataColumn}
[12] {TYPE_GUID} object {System.Data.DataColumn}
[13] {CHARACTER_MAXIMUM_LENGTH} object {System.Data.DataColumn}
[14] {CHARACTER_OCTET_LENGTH} object {System.Data.DataColumn}
[15] {NUMERIC_PRECISION} object {System.Data.DataColumn}
[16] {NUMERIC_SCALE} object {System.Data.DataColumn}
[17] {DATETIME_PRECISION} object {System.Data.DataColumn}
[18] {CHARACTER_SET_CATALOG} object {System.Data.DataColumn}
[19] {CHARACTER_SET_SCHEMA} object {System.Data.DataColumn}
[20] {CHARACTER_SET_NAME} object {System.Data.DataColumn}
[21] {COLLATION_CATALOG} object {System.Data.DataColumn}
[22] {COLLATION_SCHEMA} object {System.Data.DataColumn}
[23] {COLLATION_NAME} object {System.Data.DataColumn}
[24] {DOMAIN_CATALOG} object {System.Data.DataColumn}
[25] {DOMAIN_NAME} object {System.Data.DataColumn}
[26] {DESCRIPTION} object {System.Data.DataColumn}
[27] {PRIMARY_KEY} object {System.Data.DataColumn}
[28] {EDM_TYPE} object {System.Data.DataColumn}
[29] {AUTOINCREMENT} object {System.Data.DataColumn}
[30] {UNIQUE} object {System.Data.DataColumn}

Can anyone tell me what I've done wrong here?

回答1:

It's quite possible that SQLiteConnection.GetSchema is broken; most programs do not need this functionality.

You can get what you need by executing a PRAGMA table_info(MYTABLE) command; you should get a data reader with one row for each column.

回答2:

Here is an example of how to use the PRAGMA table_info(tableName) as suggested by Stephen Cleary to check if a specified column exists in a specified table.

/// <summary>
/// Checks if the given table contains a column with the given name.
/// </summary>
/// <param name="tableName">The table in this database to check.</param>
/// <param name="columnName">The column in the given table to look for.</param>
/// <param name="connection">The SQLiteConnection for this database.</param>
/// <returns>True if the given table contains a column with the given name.</returns>
public static bool ColumnExists(string tableName, string columnName, SQLiteConnection connection)
{
    var cmd = new SQLiteCommand("PRAGMA table_info(" + tableName + ")", connection);
    var dr = cmd.ExecuteReader();
    while (dr.Read())//loop through the various columns and their info
    {
        var value = dr.GetValue(1);//column 1 from the result contains the column names
        if (columnName.Equals(value))
        {
            dr.Close();
            return true;
        }
    }

    dr.Close();
    return false;
}

来源：https://stackoverflow.com/questions/3268986/getting-table-schema-doesnt-seem-to-work-with-system-data-sqlite

标签

sqlite

system.data.sqlite