使用sql从数据库获取记录数

Question

I am creating a test that will return the number of records in a table after I insert one record into it. The table in the database is initially empty so the count should return 1. This is the code I have written so far:

[TestMethod]
public void InsertBookIntoDb() {
    Database db = new Database();
    db.insertBooks("A", "C", "T");

    OleDbCommand countCommand = new OleDbCommand("SELECT COUNT(*) FROM Book", db.DbConnection);
    int count = countCommand.ExecuteNonQuery();

    Assert.AreEqual(1, count);
}

My db.insertBooks() method works correctly because I can manually open up the database and see that there is a new record. After running this test, the count value is always 0 no matter how many records I insert into the database. Is there a better way to get the total number of records?

Answer 1

You need OleDbCommand.ExecuteScalar

Use the ExecuteScalar method to retrieve a single value, for example, an aggregate value, from a data source.

 int count = (int) countCommand.ExecuteScalar();

Answer 2

you are using ExecuteNonQuery which is typically used for SQL statements without results (eg, UPDATE, INSERT, etc.).

we use ExecuteScalar typically when our query returns a single value. So just replace the ExecuteNonQuery' with the ExecuteScalar'. It will work correctly.

    [TestMethod]
public void InsertBookIntoDb() {
    Database db = new Database();
    db.insertBooks("A", "C", "T");

    OleDbCommand countCommand = new OleDbCommand("SELECT COUNT(*) FROM Book", db.DbConnection);
    int count = (int) countCommand.ExecuteScalar();

    Assert.AreEqual(1, count);
}