如何 map/join 两个表并使用 dapper 按参数过滤

Question

我想加入两个相互有关系的table，在客户table中，有两列用于删除和批准。获取已批准但未删除的客户，然后使用 CustId （两个表都有 CustId） 并按提供的参数过滤

将客户与贷款 table 匹配

已删除=0
批准=1

传递的参数是（并且可以是可选的）用户只能传递一个或两个或两个以上利率贷款信托日期最后付款日期

        public async Task<IEnumerable<Loan>> ManageGettingAll(string InterestRate, string LoanTrfDate, string LastPaymentDate)
        {
            IEnumerable<Loan> loans = null;

            //var sql = "Select * from MonthlyInterest where LoanAccountNo=@Id AND Deleted=@Deleted AND CAST(TranDate AS DATE) BETWEEN @StartDate AND @EndDate";
            try{

                using (var conn = new SqlConnection(connectionstring))
                {
                    await conn.OpenAsync();

                    var parameters = new 
                    { 
                        InterestRate = InterestRate, 
                        LoanTrfDate = LoanTrfDate, 
                        LastPaymentDate = LastPaymentDate
                    };
                   
                string sql = "Select l.*, c.FirstName_CompanyName from dbo.Loan l left join Customer where and l.Deleted = 0 and and l.Approved = 1 c on  l.CustId=c.CustId Where InterestRate=@InterestRate AND CAST(LoanTrfDate AS DATE)=@LoanTrfDate AND CAST(LastPaymentDate AS DATE)=@LastPaymentDate";
                 
                    loans = await conn.QueryAsync<Loan>(sql, parameters);
                }
            }
            catch (Exception ex)
            {

                throw;
            }


            return loans;
        }

Answer 1

仅当参数不为空时才按参数过滤，您可以使用下面的SQL。

Select l.*, c.FirstName_CompanyName 
from dbo.Loan l 
left join Customer c on l.CustId=c.CustId 
where l.Deleted = 0 and l.Approved = 1
and (@InterestRate is null or InterestRate=@InterestRate) 
AND (@LastPaymentDate is null or (CAST(LoanTrfDate AS DATE)=@LoanTrfDate AND CAST(LastPaymentDate AS DATE)=@LastPaymentDate))

要检查是否至少设置了一个参数，您可以添加此 if 语句。

if(string.IsNullOrWhiteSpace(LoanTrfDate) && string.IsNullOrWhiteSpace(LastPaymentDate))
{
    throw new Exception("Some clear message here.");
}

如何 map/join 两个表并使用 dapper 按参数过滤

How to map/join two tables and filter by parameters using dapper

c#

sql

sql-server

dapper

asp.net-core