C＃LINQ SQL合并转换

Question

I'm trying to convert an existing sql stored proc to use linq. The stored proc uses coalesce() while building up the 'where' clause.

Below is what I've tried.

Can some give advice / other on the correct way to approach this conversion?

------- sql

    if @a is not null 
        set @WhereClause = @WhereClause + ' and v.a_number = ''' + @a + ''''


    if @b is not null 
        set @WhereClause = @WhereClause + ' and v.b_number = ''' + @b + ''''


    if @aDateMin is not null 
        set @WhereClause = @WhereClause + ' and coalesce(v.a_end_dt, v.a_start_dt, ''1/1/1753'') 
            >= ''' + convert(varchar(10), @aDateMin, 101) + ''''


    if @aDateMax is not null 
        set @WhereClause = @WhereClause + ' and coalesce(v.a_start_dt, v.a_end_dt, ''12/31/9999'') 
            <= ''' + convert(varchar(10), @aDateMax, 101) + ''''

set @Sql =      from Results v
                @WhereClause ;';

--print @Sql
exec sp_executesql @Sql

-----linq

var aNumber = "";
var bNumber = "";
DateTime? aDateMin = null;
DateTime? aDateMax = null;

var query =     from v in searchResults
                select v;

if(!String.IsNullOrEmpty(aNumber )){
    query = query.Where(v => v.a_number == aNumber);
}

if(!String.IsNullOrEmpty(bNumber)){
    query = query.Where(v => v.b_number == bNumber);
}


//  this is where I'm having issue with the conversion.
if(aDateMin.HasValue){

    query = query.Where(v => 
                        v.a_end_dt.HasValue ? v.a_end_dt >= aDateMin : v.a_start_dt.HasValue ? v.a_start_dt <= aDateMin : "1/1/1753");

}

Answer 1

For me, using the ?? (c# equivalent of COALESCE ) might do the trick :

if(aDateMin.HasValue){
    query = query.Where(v => 
                        aDateMin.Value < v.a_end_dt ?? v.a_start_dt ?? new DateTime(1753, 1, 1));

Or another formulation :

query = query.Where(v => 
                        aDateMin.HasValue.Value < v.a_end_dt ?? v.a_start_dt ?? new DateTime(1753, 1, 1));

Answer 2

I've not tried it, but could you try something like:

var dt = new DateTime(1753, 1,1);
query = query.Where(v =>  (v.a_end_dt ?? v.a_start_dt ?? dt) >= aDateMin);