Missing PK/FK after database migration
Script out the constraints from the staging database and apply to the problem database. Lots of options, just make sure you have backups of staging and prod before you start:


Manually, one by one. Right click the objects in SSMS and opting to 'Script'.
Manually, all together (with a bit of editing). Right click database in SSMS and Tasks / Generate Scripts / Select 'Tables'. Under Scripting Options / Advanced include PK/FK. The  script created will include table definitions, you'll have to edit to leave just PK/FK.
Use a schema comparison tool to sync staging to production.
Use a script to generate the ALTER statements for you.



    SELECT
        *
        , 'ALTER TABLE ['+ FKTableSchema +'].[' + FKTableName + '] DROP CONSTRAINT ' 
            + ForeignKeyName AS FKDrop
        , 'ALTER TABLE ['+ FKTableSchema +'].[' +FKTableName + '] ADD CONSTRAINT ' 
            + ForeignKeyName + ' FOREIGN KEY(' +
          FKColumnList +') REFERENCES ['+ PKTableSchema+'].['
            + PKTableName + '] ('+PKColumnList +')' AS FKCreate
        , 'ALTER TABLE ['+ PKTableSchema +'].[' +PKTableName + '] DROP CONSTRAINT ' 
            + PrimaryKeyName AS PKDrop
        , 'ALTER TABLE ['+PKTableSchema +'].[' +PKTableName + '] ADD CONSTRAINT ' 
            + PrimaryKeyName + ' PRIMARY KEY('+PKColumnList+')' AS PKCreate
    FROM
        (
        SELECT DISTINCT
            FKTableSchema = 
                (
                SELECT DISTINCT 
                    table_schema 
                FROM 
                    INFORMATION_SCHEMA.KEY_COLUMN_USAGE 
                WHERE 
                    constraint_name=rc.constraint_Name
                ),
            FKTableName = 
                (
                SELECT DISTINCT 
                    table_Name 
                FROM 
                    INFORMATION_SCHEMA.KEY_COLUMN_USAGE 
                WHERE 
                    constraint_name=rc.constraint_Name
                    ),
            rc.constraint_name AS ForeignKeyName,
            FKColumnList = 
                (
                SELECT 
                    left(t.column_name,len(t.column_name)-1) AS 'ColumnList' 
                FROM
                    (
                    SELECT Column_Name + ',' FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
                    WHERE constraint_name=rc.constraint_name
                    FOR XML PATH('')
                    ) AS t(column_Name)
                ),
            cu.table_schema AS PKTableSchema,
            cu.table_name AS PKTableName,
            cu.constraint_Name AS PrimaryKeyName,
            PKColumnList = 
                (
                SELECT 
                    left(t.column_name,len(t.column_name)-1) AS 'ColumnList' 
                FROM
                    (
                    SELECT 
                        Column_Name + ',' 
                    FROM 
                        INFORMATION_SCHEMA.KEY_COLUMN_USAGE
                    WHERE 
                        constraint_name=cu.constraint_name
                    FOR XML PATH('')
                    ) AS t(column_Name)
                )
        FROM
            INFORMATION_SCHEMA.KEY_COLUMN_USAGE AS cu
        INNER JOIN
            INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS AS rc
        ON  rc.Unique_Constraint_name= cu.Constraint_name
    ) AS tab