Another “There is already an open DataReader associated…”

Question

Any tips how to close the DataReader ? I use postgresql and MARS is only for SQL. Or maybe I don't need MARS for this problem I don't know. The error shows in the foreach loop. Thank you for your tips.

var months = (from month in connector.PositionInstance where month.FeeNoticeMonth >= DateTime.Now.Month select month);

foreach (PositionInstance p in months)
{
    System.Windows.MessageBox.Show("" + p.First().Position.Name);
}

EDIT: i have two tables PositionInstance and Position:

CREATE TABLE "Position"
(
"PositionId" integer NOT NULL DEFAULT,
"Name" character varying(30) NOT NULL,
CONSTRAINT "PK_Position" PRIMARY KEY ("PositionId")
)

CREATE TABLE "PositionInstance"
(
"PositionInstanceId" integer NOT NULL DEFAULT,
"FeeNoticeYear" integer NOT NULL,
"FeeNoticeMonth" integer NOT NULL,
CONSTRAINT "PK_PositionInstance" PRIMARY KEY ("PositionInstanceId"),
CONSTRAINT "FK_Position_PositionInstance" FOREIGN KEY ("PositionId")
REFERENCES "Position" ("PositionId") MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION 
)

Answer 1

This problem is probably happening in your case due to lazy loading, which is happening inside of the foreach loop. It's trying to load each Position from the DB on each iteration of the loop.

One way around this is to use eager loading to get all the Positions at once in your query. Then if you also use a greedy operation such as ToList() at the end of your query, the DB is executed and everything is pulled in one go. In your case try something like

var months = 
    (from month in connector.PositionInstance 
     where month.FeeNoticeMonth >= DateTime.Now.Month 
     select month).Include("Position").ToList();

or some variation. Using use the ToList() after the query will type variable months as a List (which is an IEnumerable ) containing the populated results from the DB; otherwise months will be an IQueryable with the DB query not yet executed.

Answer 2

try to add this in the connection string:

MultipleActiveResultSets=True