Prevent multiple duplicate data entry into entities database

I am trying to prevent a duplicate data entry into the entity database when inserting into the database. Currently heres my code for inserting into database. I have check many post online but not really sure which one to use as it seems really different. I am trying to prevent duplicate entry for PatientIc and display an error message for it. Thanks in advance!

protected void myGridview_RowCommand(object sender, GridViewCommandEventArgs e)

{

//Insert new Prescription

if (e.CommandName == "Insert")

{

Page.Validate("Add");

if (Page.IsValid)

{

var fRow = myGridview.FooterRow;

TextBox txtPatientName = (TextBox)fRow.FindControl("txtPatientName");

TextBox txtPatientIC = (TextBox)fRow.FindControl("txtPatientIc");

TextBox txtQuantity = (TextBox)fRow.FindControl("txtQuantity");

DropDownList ddType = (DropDownList)fRow.FindControl("ddType");

DropDownList ddState = (DropDownList)fRow.FindControl("ddState");

using (CareGiverEntities dc = new CareGiverEntities())

{

dc.Contacts.Add(new Contact

{

PatientName = txtPatientName.Text.Trim(),

PatientIc= txtPatientIC.Text.Trim(),

Quantity = txtQuantity.Text.Trim(),

MedicineTypeID = Convert.ToInt32(ddType.SelectedValue),

MedicineID = Convert.ToInt32(ddState.SelectedValue),

DatePrecribed= DateTime.Now

});

dc.SaveChanges();

PopulateContacts();

}

}

}

}

Codes for Grid view

DataKeyNames="ContactID,MedicineTypeID,MedicineID" CellPadding="10" CellSpacing="0"

ShowFooter="true"

CssClass="myGrid" HeaderStyle-CssClass="header" RowStyle-CssClass="trow1"

AlternatingRowStyle-CssClass="trow2" OnRowCommand="myGridview_RowCommand" OnRowCancelingEdit="myGridview_RowCancelingEdit" OnRowDeleting="myGridview_RowDeleting" OnRowEditing="myGridview_RowEditing" OnRowUpdating="myGridview_RowUpdating" AllowPaging="True" AllowSorting="True" >

No results found.

Patient Name

<%#Eval("PatientName") %>

Display="Dynamic" ValidationGroup="edit" ControlToValidate="txtPatientName">Required

ForeColor="Red" Display="Dynamic" ValidationGroup="Add" ControlToValidate="txtPatientName">Required

Patient IC

<%#Eval("PatientIc") %>

Display="Dynamic" ValidationGroup="edit" ControlToValidate="txtPatientIc">Required

ForeColor="Red" Display="Dynamic" ValidationGroup="Add" ControlToValidate="txtPatientIC">Required

Quantity

<%#Eval("Quantity") %>

Display="Dynamic" ForeColor="Red" ValidationGroup="edit" ControlToValidate="txtQuantity">Required

ForeColor="Red" Display="Dynamic" ValidationGroup="Add" ControlToValidate="txtQuantity">Required

Medicine Type

<%#Eval("MedicineType") %>

OnSelectedIndexChanged="ddCountry_SelectedIndexChanged">

ForeColor="Red" Display="Dynamic" ValidationGroup="edit" ControlToValidate="ddType" InitialValue="0">

Required

ForeColor="Red" Display="Dynamic" ValidationGroup="Add" ControlToValidate="ddType" InitialValue="0">Required

Medicine Name

<%#Eval("MedicineName") %>

ForeColor="Red" Display="Dynamic" ValidationGroup="edit" ControlToValidate="ddState" InitialValue="0">

Required

ForeColor="Red" Display="Dynamic" ValidationGroup="Add" ControlToValidate="ddState"

InitialValue="0">Required

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