Important table methods in Dynamics 365 for Finance and Operations

public class POLMobileServiceTable extends common
{
    
    /// 

    /// When i initialize a record, this method will be triggered
    /// This method is not responsible for saving the record to database
    /// Rather it assigns value to BUFFER
    /// 
    public void initValue()
    {
        super();

        this.ServiceStartDate       = systemDateGet();
        this.ExpectedDeliveryDate   = systemDateGet() + 5;
    }

    /// 

    /// Validate delivery date and service amount
    /// 
    /// 
    public boolean validateWrite()
    {
        boolean ret;
    
        ret = super();

        //If all the previous valdiations have passed?
        if (ret)
        {
            //Then check for the date validation
            if (this.ServiceStartDate > this.ExpectedDeliveryDate)
            {
                //error("Expected delivery date cannot be lesser than service start date.");
                //ret = false;

                ret = checkFailed("Expected delivery date cannot be lesser than service start date.");
            }

            //If all the previous valdiations have passed?
            if (ret && this.ExpectedServiceAmount <= 0)
            {
                ret = checkFailed("Expected service amount should be specified.");
            }
        }
    
        return ret;
    }

    /// 

    ///
    /// 
    /// 
    public boolean validateDelete()
    {
        boolean ret;
    
        ret = super();

        if (ret)
        {
            if (this.ServiceStatus == POLServiceStatus::Delivered)
            {
                ret = checkFailed("Service status with Delivered, cannot be allowed to delete.");
            }
        }
    
        return ret;
    }

    /// 

    ///
    /// 
    /// 
    public void modifiedField(FieldId _fieldId)
    {
        super(_fieldId);

        switch(_fieldId)
        {
            case fieldNum(POLMobileServiceTable, ModelID):
                //1st way
                //if (this.ModelID == "Samsung")
                //{
                //    this.ExpectedServiceAmount = 2000;
                //}
                //else if (this.ModelID == "Sony")
                //{
                //    this.ExpectedServiceAmount = 1500;
                //}
                //else if (this.ModelID == "Apple")
                //{
                //    this.ExpectedServiceAmount = 3000;
                //}

                //2nd way
                //POLModelTable  polModelTable;

                //select * from polModelTable
                //    where polModelTable.ModelID == this.ModelID; //current selection

                //3rd way
                //POLModelTable  polModelTable = POLModelTable::find(this.ModelID);
                //this.ExpectedServiceAmount = polModelTable.MinimumServiceAmount;

                //best way for writing
                this.ExpectedServiceAmount = POLModelTable::find(this.ModelID).MinimumServiceAmount;
                break;
        }
    }

    /// 

    ///
    /// 
    public static POLMobileServiceTable find(POSServiceID _serviceID, boolean _forUpdate = false)
    {
        POLMobileServiceTable polMobileServiceTable;

        if (_serviceID)
        {
            polMobileServiceTable.selectForUpdate(_forUpdate);

            select * from polMobileServiceTable
                index hint ServiceIdx
                where polMobileServiceTable.ServiceID == _serviceID;
        }

        return polMobileServiceTable;
    }

}