Converting conditionally built SQL where-clause into LINQ
So I didn't see a question here that really answers this question. It's kinda a newbie question about linq but I would like to know if it would be possible to convert the following sql query (built using C#) into a linq query:
public void DoSomeQuery(bool whereCriteria1, bool whereCriteria2)
{
string sqlQuery = "SELECT p.*";
string fromClause = " FROM person p";
string whereClause = " WHERE ";
if (whereCriteria1)
{
fromClause += ", address a";开发者_C百科
whereClause += " p.addressid = a.addressid and a.state = 'PA' and a.zip = '16127' "
}
if (whereCriteria2)
{
fromClause += ", color c";
whereClause += " p.favoritecolorid = c.colorid and c.name = 'blue'"
}
// arbitrarily many more criteria if blocks could be here
sqlQuery += fromClause + whereClause;
// do stuff to run the query
}
Does that make sense? I have a bunch of bool variables that let me know which where clause criteria to add. I want to do that in linq because well ... this is ugly.
var query = from p in persons select p;
if (whereCriteria1)
{
query = from p in query
join a in address on p.addressid equals a.addressid
where a.state = 'PA'
where a.zip = '16127'
select p;
}
if (whereCriteria2)
{
query = from p in query
join c in colors on p.favoritecolorid equals c.colorid
where c.name = 'blue'
select p;
}
You're looking for dynamic predicates built at runtime. Here is a good CodeProject article.
You may also be interested in this PredicateBuilder.
Sure, the answer is similar to the one I provided for this question. The basic strategy is to define your "base query" and then to conditionally add where clauses to the query.
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